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Transportation Research Board National Research Council NAS1 NAfl lQ
Special Report 223 Providing Access For. LARGE. TRUC16 Transportation Research Board National Research Council Washington, D.C. 1989
Transportation Research Board Special Report 223 mode 1 highway transportation subject areas 12 planning 51 transportation safety . 53 vehicle characteristics Transportation Research Board publications are available by ordering directly from TRB. They may also be obtained on a regular basis through organizational or individ- ual affiliation with TRB; affiliates or library subscribers are eligible for substantial discounts. For further information, write to the Transportation Research Board, National Research Council, 2101 Constitution Avenue, N.W., Washington, D.C. 20418. Printed in the United States of America NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competencies and with regard for appropriate balance. This report has been reviewed by a group other than the authors according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. This study was sponsored by the Federal Highway Administration of the U.S. Department of Transportation. Library of Congress Cataloging-in-Publication data available: LC card number 89-12600. Cover Design: Karen White Shaeffer
Committee for Truck Access Study ROLAND A. OUELLETFE, Eno Foundation for Transportation, Inc., Westport, Connecticut, Chairman ROBERT G. ADAMS, California Department of Transportation, Sacramento CARLA J. BERROYER, Illinois Department of Transportation, Springfield BYRON C. BLASCHKE, Texas Department of Highways and Public Transportation, Austin JOHN W. BOORSE, City of Philadelphia, Pennsylvania S. EARL DovE, AAA Cooper Transportation, Dothan, Alabama WILLIAM D. GLAUZ, Midwest Research Institute, Kansas City, Missouri JEROME W. HALL, University of New Mexico, Albuquerque GEORGE W. HERNDON, Florida Department of Transportation, Tallahassee VA1' CLEVE HOLMES III, Maryland State Police, Pikesville DONALD F. KUSTER, Continental Can Co., Inc., Oak Brook, Illinois HAROLD L. MICHAEL, Purdue University, West Lafayette, Indiana WILLIAM A. PHANG, Pavement Management Systems, Amherst, New York JAMES P. RAK0w5KI, Memphis State University, Tennessee MICHAEL J. RIGHT, Automobile Club of Missouri, St. Louis CHESTER STRANCZEK, Cresco Lines, Inc., Crestwood, Illinois GERALD H. STREICHERT, Shiawassee County Road Commission, Corunna, Michigan CHARLES V. ZEGEER, University of North Carolina, Chapel Hill Liaison Representatives ARTHUR J. BALEK, Federal Highway Administation, U.S. Department of Transportation WILLIAM DRUHAN, American Association of State Highway and Transportation Officials, Washington, D.C.
BARBARA HARSHA, National Association of Governors' Highway Safety Representatives, Washington, D.C. JAMIE MCLAUGHLIN FISH, Committee on Public Works and Transportation, U.S. House of Representatives N.tmn HAMILTON, Committee on Environment and Public Works, U.S. Senate KENNETH HOUSE, Committee on Public Works and Transportation, U.S. House of Representatives JEAN LAUVER, Committee on Environment and Public Works, U.S Senate JOHN L. REITH, American Trucking Associations, Alexandria, Virginia Transportation Research Board Staff ROBERT E. SKINNER, JR., Director for Special Projects NANCY HUMPHREY, Project Manager THOMAS MENZIES, Research Associate ELAINE KING, Division A Liaison NANCY A. ACKERMAN, Director of Publications ELIZABETH W. KAPLAN, Associate Editor
Preface THE SURFACE TRANSPORTATION ASSISTANCE ACT of 1982 expanded the federal role in regulating the size of heavy commercial vehicles and introduced the concept of a designated National Network of major trunk roads for heavy truck travel. Controversy ,over the extent of "reasonable access" that could safely be provided off this National Net- work to the longer and wider vehicles authorized by the act gave rise to the congressional mandate for this study. To carry out the study, the Transportation Research Board (TRB) formed a committee under the leadership of Roland A. Ouellètte, Presi- dent of the Eno Foundation for Transportation, Inc. Committee members are technical experts on highway safety, traffic operations, highway de- sign, pavements, and freight transportation economics as well as practi- tioners who represent state and local transportation departments, law enforcement agencies, the motor carrier industry, and shippers. The results of the committee's study and recommendations for a national policy on "reasonable access" are presented here. One committee mem- ber, William A. Phang, was unable to complete the final report review and sign off because of serious illness. Another committee member, Donald F. Kuster, was unable to approve the committee's report. Nancy Humphrey managed the study and, with Thomas Menzies, drafted the final report under the guidance of the committee and the overall supervision of Robert E. Skinner, Jr., Director for Special Proj- eëts. Special appreciation is expressed to Nancy A. Ackerman, TRB Director of Publications, and Elizabeth W. Kaplan, Associate Editor, for editing and publishing the final report, and to Marguerite E. Schneider and Frances E. Holland for assistance in typing drafts of the manuscript.
Contents Executive Summary . 1 Introduction ............................................ 9 Legislative Mandate for This Study, 10 Scope of Study, 11 Organization of Report, 13 2 Historical and Regulatory Overview ........................ 15 Truck Size Regulations, 15 Implementation of Access Provisions of the STAA, 20 Characteristics of and Experience with STAA Vehicles, 22 Effect of 1982 STAA 'on Volume of Truck Traffic, 25 3 Current Access Policies and Practices....................... 31 Extent of Highways Open to STAA Vehicles, 32 State Access Provisions, 44 Local Access Provisions, 54 Summary of Findings, 59 4 STAA Vehicle Use and Productivity ........................ 65 Characteristics and Structure of the Trucking Industry, 66 Uses and Benefits of STAA Vehicles, 74 Impact of Truck Access Policies, 84 Summary Assessment, 89 5 Safety: Accident Studies .................................. 95 Overview of Combination Vehicle Safety and Travel, 96 Comparative Accident ExperienceâSTAA Versus Non-STAA Vehicles, 99 Accident Experience by Road 1'pe and Characteristics, 111 Summary and Findings, 121
6 Highway Design and Accident Risk ........................127 Important Geometric Features, 128 Relationship Between STAA Vehicle Operating Characteristics and Highway Geometric Features, 130 Findings, 149 Implications for Developing Access Policies, 151 7 Traffic Operations and Safety ............................. 155 Measuring the Impact of Heavy Trucks on Highway Capacity, 156 Factors Affecting STAA Vehicle Impact on Traffic Operations, 157 Summary, 167 8 Highway Condition ....................................... 171 Pavements, 172 Bridges and Culverts, 188 Highway Shoulders and Appurtenances, 191 Summary, 193 9 Summary Assessment .................................... 197 Policy Alternatives, 197 Need for Common Procedures for Providing Access, 199 Characteristics of a Process for Reviewing Roads for Access, 200 Regulating Offtracking, 203 Local Government Access Policies, 206 Implementation of Access Policies, 207 Definition of Terminal, 208 Monitoring the Performance of STAA Vehicles, 210 Conclusion, 210 Appendix A Federal Legislation Mandating the Truck Access Study......................................... 213 Appendix B Sections of Highway Laws Relating to TruckSize..................................... 217 Appendix C Questionnaires and Detailed Tables for Chapter3 ..................................... 225 Appendix D Carrier and Shipper Surveys .................... 259 Appendix E OtTtracking .................................... 281 Appendix F Pavement Rehabilitation Cost Model .............. 303 Appendix G Dissenting Statement ........................... 309
Executive Summary S TATES HAVE REGULATED the size of commercial vehicles since the early 1900s. The trends have been toward ever larger trucks, mirroring improvements in the highway system and vehi- cle technology, and toward growth in the volume of freight moved by trucks. Increases in vehicle size have yielded substantial improvements in productivity but have also raised concern about the safety of truck travel and the compatibility of large trucks with the nation's highway system. The Surface Transportation Assistance Act (STAA) of 1982 attempted to strike a balance between improved efficiency of trucking operations and safety. It expanded the federal role in commercial motor vehicle size regulation by preempting state regulations and liberalizing restrictive limits in many states. It also authorized the U.S. Secretary of Transporta- tion to designate a National Network of Interstate and other major highways on which the wider (102-in.) and longer tractor-semitrailers (minimum trailer length 48 ft) and twin trailer (minimum trailer length 28 ft) trucks approved by the act (STAA vehicles) could travel without restriction. The act also required states to provide "reasonable access" from this network to terminals and facilities for food, fuel, repairs, and rest (service facilities); the implementing regulations entrusted to the states the determination of where such access could safely be provided. Since the act became law, the U.S. Department of Transportation has designated a National Network and all states have enacted access policies. Because of the restrictiveness of some state access policies, carriers and shippers have petitioned the Federal Highway Administration (FHWA) to establish minimum uniform standards for reasonable access. State and local transportation officials, however, maintain that access decisions should be made locally. To help resolve these differences, the Congress, acting through the Surface Transportation and Uniform Relocation and 1
PROVIDING ACCESS FOR LARGE TRUCKS Assistance Act of 1987, requested that the Transportation Research Board of the National Research Council conduct a study on a nationwide policy for provision of reasonable access. The study committee considered several policy options, including uni- form standards for access based on such factors as distance from the National Network, type of highway, and roadway characteristics. It drew on research studies and information provided by representatives of state and local highway and transportation departments, state trucking asso- ciations, carriers, and shippers about the effects of travel by large trucks, particularly STAA vehicles, on access roads. SUMMARY OF MAJOR FINDINGS AND RECOMMENDATIONS Summaries of the major findings and recommendations follow. Procedures for Determining Appropriate Highways for Access Findings Local highway and traffic conditions differ from state to state and from route to route; these differences make a single national standard for determining access inappropriate. Disagreements between states and industry on access are concen- trated in a small number of states, although lack of rigorous enforcement of access regulations may partly explain the absence of more widespread problems. The proportion of mileage open to STAA vehicles for through travel and access varies widely among the states; some states appear to have overly restricted STAA vehicle travel without basing their policies on sound safety and engineering considerations. Some highways, however, cannot accommodate STAA vehicles or any other large combination vehicles. Decisions to limit or not limit access should be based on safety- related differences between STAA vehicles and the vehicles they replace, including such factors as vehicle maneuverability on curves and at inter- sections and the effect of vehicle length on sight distance for passing and at intersections. 0 Determining appropriate highways for access requires judgments
Executive Summary about the adequacy of specific highway design features in relation to the operating performance of STAA vehicles; the tools for making these assessments are available. Recommendation The FHWA should require states to adopt and use procedures based on safety and engineering considerations to assess the adequacy of highways to accommodate STAA vehicles. The FHWA should review and certify these procedures. States that have established procedures that differ from those recommended but that accommodate government and industry concerns about access could petition FHWA for certification of their current procedures. Safety Findings Congress identified safety as the primary criterion for access deter- mination, but little information is available about the accident experience of STAA vehicles relative to that of the vehicles they replace. Most available studies focus on the accident record of twin trailer trucks compared with tractor-semitrailers and find little difference in accident rates of the two vehicle configurations. No studies were found that compared the accident record of STAA tractor-semitrailers with that of tractor-semitrailers of pre-STAA dimensions. (Several organizations are working to fill the gap in information about the safety of large trucks, and the committee endorses timely completion of these efforts.) Accident rates of trucks are most affected by the type of road on which trucks travel; accident rates are lowest on roads designed to the highest standards. Recommendation State and local governments should strive to open to STAA vehicle travel the maximum practical number of miles of their through-travel and access roads, particularly those constructed to the highest design standards, that meet the safety and engineering criteria recommended in this report.
PROVIDING ACCESS FOR LARGE TRUCKS Vehicle Handling Characteristics Findings The safety of STAA vehicles cannot be determined directly from accident records but can be examined by assessing the handling and performance of the longer and wider STAA vehicles on highways with different geometric characteristics. Offtracking is the performance characteristic that is the most no- ticeably and measurably different for STAA and pre-STAA vehicles. Inward offtracking occurs during turning maneuvers, generally made at speeds below 35 to 40 mph, on curves and at intersections. The rear wheels of a truck-trailer unit swing inside the path of the front tractor wheels with the result that the driver is likely to "cut" the corner or swing wide into the adjacent lane to stay on the road. At low speeds, twin trailer trucks offtrack less, and thus maneuver better, than the tractor-semitrailers of pre-STAA dimensions they replace. A properly configured STAA tractor-semitrailer can approximate the offtracking characteristics of a pre-STAA tractor-semitrailer; thus the miles of highways that may be considered as candidates for through travel and access by STAA tractor-semitrailers may be increased. The amount of inward offtracking of semitrailers is affected by the dimensions of the vehicle. The dominant dimension is the distance from the kingpin to the center of the rear trailer axle or axles. Some states have imposed maximum kingpin-to-rear-axle limits on the longer STAA tractor-semitrailers (i.e., trailer lengths ranging from 50 to 59.5 ft were "grandfathered" by the 1982 STAA in 25 states) to reduce inward offtracking and improve their operating performance relative to that of the vehicles they replace. States have made different interpreta- tions of the provisions of the 1982 STAA with respect to their authority to impose these restrictions on the National Network and its connecting access routes. A proliferation of different state-required kingpin settings for STAA tractor-semitrailers could reduce carrier compliance and complicate enforcement. The increase in STAA vehicle length has a greater effect on STAA vehicle performance than the 6-in. increase in vehicle width from 96 to 102 in. The increase in width has only a minor effect on the safe operation of STAA vehicles, except on narrow lanes of 10 ft or less.
Executive Summary Recommendation The committee urges the Congress to clarify whether states have the authority to restrict kingpin-to-rear-axle dimensions on the National Net- work as well as its access routes under the provisions of the STAA. A small majority of the committee further recommend that all states be encour- aged to adopt a maximum kingpin setting of 41 ft (measured from the kingpin to the center of the rear trailer axle or group of axles) on their National Network highways and access routes if Congress indicates that states have this authority. Every effort should be made to expedite FHWA encouragement of state acceptance of this kingpin setting as a criterion for evaluating access routes. Several other committee members proposed stronger action, recommending that all states be required to adopt a maximum kingpin setting of 41 ft and that the FHWA be directed to include this setting in the final rulemaking on access. This kingpin setting should also be included in FHWA regulations that apply to National Network highways as well as access routes if Congress indicates that states have the authority to restrict kingpin-to-rear-axle dimensions on these roads. The 41-ft setting, which would make the maneuverability of the longer STAA semitrailers equivalent to that of the 48-ft STAA semitrailer (with its rear trailer axle or axles in the farthest back position), was selected as a practical compromise because the 48-ft unit is becoming the industry-standard semitrailer. Pavement Service Life Finding STAA vehicle traffic, particularly the potentially more damaging fully loaded twin trailer truck, reduces pavement life. The incremental in- crease in pavement rehabilitation costs can range from 7 percent to a worst case 15 percent on access roads designed for some large truck traffic, depending on the volume and mix of the truck traffic and pave- ment conditions. Recommendation The impact of vehicle size and weight changes on the life of pavements on access highways should be considered when future modifications of legal truck sizes and weights are evaluated.
PROVIDING ACCESS FOR LARGE TRUCKS Access to Service Facilities Finding Providing access to service facilities has not been raised as a problem by government or industry. Many states now allow STAA vehicles to travel a short distance, generally ranging from 1 to 3 mi, from the National Network to reach service facilities. The committee believes that safety should be the primary consideration in providing access; it concluded, however, that unless safety problems are identified, allowing short dis- tance limits to service facilities is sensible because it would be impractical and of limited value to require states to evaluate all of these short road segments. Recommendation States should provide a distance-based access limit of at least 1 mile to service facilities. States may deny access to service facilities on roads that are deemed inappropriate for STAA vehicles because of safety and engi- neering considerations but should provide access to other service facilities within a reasonable distance. Local Government Access Policies Findings Local governments have jurisdiction over many miles of highways and, in 18 states, have independent authority to establish access policies. Many local governments have limited resources and technical knowl- edge about the handling and performance of STAA vehicles; thus the potential exists for an even wider disparity of access policies at the local than at the state level. Recommendation States should take a leadership role in providing assistance to local gov- ernments as they establish access policies. States should provide local governments with criteria to consider in developing access policies; pro-
Executive Summary vide technical information that is pertinent to evaluating access requests; and, as required, coordinate industry requests for access that involve local government review, establish a time frame for completion of reviews, and create mechanisms for resolving conflicts. Implementation of Access Policies Finding Access restrictions are generally not perceived as arbitrary when clear evaluation criteria are applied in a timely and consistent manner. Recommendation Requests for continuing access should be reviewed by state and local governments in a timely manner. Thirty days or less is a reasonable period for processing access applications. Access should be approved automat- ically if applications are not reviewed in 90 days. When a state grants access approval for one type of STAA vehicle, this approval should apply to all vehicles of that type regardless of who owns or operates them. Definition of "Terminal" Findings In the absence of a specific definition of the word "terminal" in the 1982 STAA and implementing federal regulations, some states have adopted a narrow definition that unduly restricts access on roads that could be designated for access on the basis of the criteria established in this study. A definition of "terminal" is needed to maintain the distinction between roads built for high volumes of through truck traffic and roads built to lower design standards that are intended for the more limited purpose of providing access. Recommendation "Terminal" should be defined as any location where (a) freight either originates, terminates, or is handled in the transportation process or (b)
PROVIDING ACCESS FOR LARGE TRUCKS carriers maintain operating facilities. This definition is not intended to supersede existing bans or preclude new bans on combination truck travel, such as those on through travel on residential streets, weight- posted roads or bridges, or roads not deemed appropriate for access on the basis of safety and engineering considerations. CONCLUSION The access issue reflects the difficulty of balancing pressures for improved efficiency in trucking operations with the inadequacies of the existing highway network to accommodate large-truck travel. The concept of restricting truck travel to a network of the nation's "best" highways represents an attempt to balance productivity and safety but is difficult to implement because a vast majority of carriers need to travel beyond the designated routes. Many transportation officials believe that the highway system, particularly roads built to lower standards than the Interstate system, is at the limit of its ability to accommodate large trucks. However, it is difficult to document the adverse impacts of small increments in vehicle size on safety and traffic operations and to identify all of the relevant costs that are implicit in a change in vehicle size regulations. The committee believes that, if vehicle size regulations are revised in the future, the concept of a designated National Network should be carefully reevaluated and the cost implications more thoroughly considered.
1 Introduction T HE U.S. ECONOMY DEPENDS heavily on trucks for moving goods and materials. In 1987, the latest year for which informa-tion is available, trucking accounted for nearly one-third of all domestic intercity freight traffic, measured in ton-miles,' and nearly three-fourths of the nation's intercity freight bill (Transportation Policy Associates 1988, 4). The growth of commercial trucking reflects, in large part, improve- ments in the nation's highway system. Completion of major segments of the Interstate highway system in the early 1970s provided a major boost to the use of trucks to transport freight. Travel by commercial truck has continued to grow ever since. Between 1979 and 1987, vehicle-miles traveled by combination trucks (the most common type of intercity freight vehicle) increased by nearly 30 percent (Highway Statistics 1979 1980, 138 and Highway Statistics 1987 1988, 171), while vehicle-miles traveled by passenger cars grew by only 19 percent. Truck travel is projected to grow at twice the rate of peronal vehicle travel in the future (Highway Users Federation 1988, 29). The size and weight of trucks have also grown as industry has sought greater operating efficiencies. The federal government first established maximum limits on commercial vehicle size and weight as part of the Federal-Aid Highway Act of 1956, which authorized the Interstate con- struction program. These regulations, however, applied only to Interstate highways. The states, which had imposed vehicle size and weight limits since the early 1900s, retained wide latitude in setting these standards for other roads. The Surface Transportation Assistance Act (STAA) of 1982 attempted to introduce greater uniformity in vehicle size and weight regulations but at the same time required that heavy trucks pay a substantial share of the 9
10 PROVIDING ACCESS FOR LARGE TRUCKS proposed motor fuel tax increases. The federal regulations preempted more restrictive state vehicle size and weight limits and liberalized various vehicle size and weight provisions. However, the regulations limited travel by vehicles of the dimensions authorized by the act (STAA vehicles) to a National Network that was to be designated by the U.S. Secretary of Transportation. This National Network was to comprise Interstate high- ways and significant portions of other primary highways built to accom- modate large-truck travel.2 States were to provide reasonable access beyond the National Network to terminals and facilities for food, fuel, repair, and rest (i.e., service facilities). An exception was made for household goods carriers, who were granted unlimited access to points of loading and unloading. Since passage of the 1982 STAA, the trucking industry has sought to make full use of the productivity potential of the larger equipment al- lowed by the act. Competitive pressures introduced by the Motor Carrier Act of 1980, which deregulated many aspects of the trucking industry; the recession of the early 1980s, which squeezed industry profit margins; and the more recent shortage of truck drivers have created strong incentives to seek improvements in productivity. The trend toward larger vehicles and projections of increased truck travel, however, have raised questions from the safety community and highway engineers about the extent to which the highway system can accommodate this travel safely as well as its impacts on traffic operations and highway condition. Of particular concern is truck access on highways off the National Network that have more diverse road conditions and may not be built to the design standards of the National Network. LEGISLATIVE MANDATE FOR THIS STUDY In response to the continuing debate over an appropriate balance be- tween productivity and safety, Section 158 of the Surface Transportation and Uniform Relocation Assistance Act of 1987 (Appendix A) mandated that the Transportation Research Board (TRB) of the National Research Council conduct a study on the establishment of a nationwide policy for provision of "reasonable access" to the National Network for the longer and wider combination vehicles. TRB is also performing a related study on truck weight issues, including the federal bridge formula and grand- father provisions.3 Section 158 requested that TRB examine the various positions of government and industry regarding truck access and provide estimates of the impacts of alternative policies on highway safety, pavements and bridges, highway revenue and cost responsibility, and transportation
Introduction11 costs or other measures of productivity for various segments of the trucking industry. As appropriate, related issues of permitting, enforce- ment, and data availability and reliability may be addressed. The Confer- ence Report accompanying the Continuing Resolution of December 1987 (U.S. House of Representatives Report No. 100-498) also recommended that the TRB study provide a definition of "terminal" (Appendix A). The report further directed the Federal Highway Administration, which had issued an advance notice of proposed rulemaking on truck access, to refrain from issuing a final rule until the TRB had completed its study and to make safety the most important consideration in any subsequent rulemaking on access. SCOPE OF STUDY In response to the congressional mandate, TRB formed a study commit- tee on access made up of technical experts on highway safety and traffic operations, highway design and pavements, and freight transportation economics and practitioners representing state and local transportation departments, commercial motor vehicle enforcement agencies, the motor carrier industry, and shippers. The committee's mandate was to make recommendations for a national policy on truck access. Developing an appropriate strategy for access required that two basic tasks be performed. First, current access policies and problems were reviewed to define the nature and extent of access problems; to characterize the key approaches to, and key issues involved in, access from the perspective of state and local governments and indus- try; and to identify examples of policies for providing reasonable access that accommodate the concerns of government and industry. This part of the study drew heavily on surveys, site visits, and telephone interviews for information on current state and local government access policies and the impact of these policies on the trucking industry and shippers. Second, what is known about the impacts of STAA vehicle operation on access roads was reviewed. Impacts on productivity, safety, highway design, traffic operations, and highway condition were considered. Productivity The primary objective of industry in seeking broader access for STAA vehicles is the productivity gain to be reaped from the widest possible use of these vehicles. Thus a major task of the study committee was to identify how carriers and shippers use, or would like to use, STAA vehicles; the
12 PROVIDING ACCESS FOR LARGE TRUCKS key benefits of their use; the extent to which state and local access policies restrict their use; and the costs of these restrictions. Safety Congress identified safety as the primary criterion to guide access deci- sions. A key issue in determining the extent of access that should be granted is the accident performance of STAA vehicles compared with that of the vehicles they replace (i.e., combination vehicles of pre-1982 STAA dimensions). The limited operating history of certain vehicle configura- tions; inadequate accident reporting; and lack of information on vehicle- miles traveled by truck configuration, which would allow computation of accident rates, limit the availability and the reliability of many data sources. However, national truck accident data and safety studies were reviewed to determine what is known about the safety record of STAA vehicles. Highway Design Another way to assess the performance of STAA vehicles is to examine their handling and performance characteristics in relation to the geomet- ric characteristics of the roads on which they are likely to travel. Although it is not possible to establish a direct correlation between handling and performance characteristics and increased accident rates, the combina- tion of some of these characteristics and poorly designed roads is likely to increase accident risk. A review was undertaken of what is known about the relationship between the operating characteristics of STAA vehicles and some important geometric features of highways. The purpose was to identify the vehicle characteristics and geometric conditions that pose the most serious problems for STAA vehicles compared with the vehicles they replace. Traffic Operations Another area of concern in allowing STAA -vehicles broad access from Interstate and other primary highways designated for their travel is the degradation in service quality that may result from congestion and delays caused by increased STAA vehicle travel on access roads. Studies were reviewed to determine what is known about STAA vehicle impact on
Introduction 13 traffic operations under various traffic and highway conditions. Pro- jections of the expected volume of STAA traffic by road type were not developed, but information about the expected use of STAA vehicles was drawn from interviews with motor carriers and shippers; segments of the industry most likely to increase their use of STAA vehicles were identi- fied; and implications for travel on access roads were defined. Highway Condition A final concern in allowing STAA vehicles broad access is the added wear and tear they may cause to highways, bridges and culverts, and highway appurtenances. Because pavement life is directly related to vehicle axle loads, TRB's truck weight study3 addresses these issues in depth. How- ever, this study attempts to define more precisely the impacts of STAA vehicle travel on the service life of pavements and structures typical of access roads, drawing on other studies when relevant and quantifying when possible the effects on rehabilitation costs of any identified reduc- tion in service life. The issue of highway revenue and cost responsibility was not examined in detail. Because of the wide disparity among states in both the extent of access provided and the range of vehicles that were legal both before and after passage of the 1982 STAA, it was not possible to quantify precisely the incremental impacts of alternative access policies. However, it was noted that the costs of providing reasonable access may not have been fully recognized when the 1982 STAA was enacted and that these costs should be more thoroughly examined before any future changes are made in federal size regulations. ORGANIZATION OF REPORT The results of the study are presented in the following chapters. Chapter 2 is a review of the historical and regulatory background of the truck access issue. In Chapter 3 current access policies and practices are summarized to define the nature and extent of the problem and to provide examples of alternative policy approaches. Chapters 4 through 8 are an examination of what is known about the impacts of STAA vehicle operation on produc- tivity, safety, highway design, traffic operations, and highway condition, respectively. The relevant literature ' is reviewed to identify key findings about the operation of STAA vehicles, to determine the relative magni- tude of their impact, and to draw implications for developing access
14 PROVIDING ACCESS FOR LARGE TRUCKS policies. In the final chapter the pros and cons of alternative access policies are compared in light of these impact assessments and recommen- dations are provided on minimum requirements for access that, in the judgment of the committee, will assure a reasonable balance between safety and productivity. NOTES A ton-mile is defined as the movement of 1 ton (2,000 ib) of freight the distance of 1 mi. Note that freight moved by air and pipeline is not included. The primary system consists of Interstate highways and other major arterial high- ways that connect cities and centers of industrial activity. In response to the congressional mandate, TRB has convened two committees: one to address truck weight issues and the other, which is responsible for this study, to address the circumstances under which the longer and wider vehicles authorized by the 1982 STAA should be permitted to travel beyond the National Network to reach terminals and service facilities. REFERENCES ABBREVIATION FHWA Federal Highway Administration Highway Statistics 1979 and 1987. 1980, 1988. FHWA, U.S. Department of Transportation. Highway Users Federation. 1988. Beyond Gridlock. The Advisory Committee on Highway Policy of the Transportation 2020 Program, Washington, D.C. Transportation Policy Associates. 1988. Transportation in America. Washington, D.C. U.S. House of Representatives Report No. 100-498. 1987. Conference Report on House Joint Resolution 395. 100th Cong., 1st Sess., Dec. 21.
2 Historical and Regulatory Overview T RUCK ACCESS BECAME AN ISSUE after passage of the Surface Transportation Assistance Act (STAA) of 1982. How-ever, the issue has its antecedents in a long history of state and federal vehicle size and weight regulations. This chapter provides a brief review of truck size regulations; a summary of the major related provi- sions of the 1982 STAA;' a discussion of implementation of the STAA access provisions, including recent litigation; a description of the charac- teristics of, and experience with, vehicles of the dimensions authorized by the 1982 act; and an examination of the impact of the STAA on the volume of truck traffic. TRUCK SIZE REGULATIONS Although the 1982 STAA represents a major expansion of the federal role in truck size regulation, it must be viewed as another stage, albeit a major one, in the nearly 70-year history of state and federal regulation of commercial motor vehicle size. The dominant trend has been toward larger trucks, mirroring improvements in the highway system and vehicle technologies. The costs and benefits of each revision in size regulations have been assessed in terms of the incremental impacts on freight trans- portation and highway safety and condition. The cumulative effect of these changes has been to improve substantially the efficiency of freight transportation by truck.2 However, it has become increasingly difficult for certain highways, particularly those that are not built to current stan- dards, to accommodate ever larger equipment. When viewed in this 15
16 PROVIDING ACCESS FOR LARGE TRUCKS broader context, the liberalization of truck size regulations authorized by the 1982 STAA and the related question of truck access become simply another step in a continuing effort to balance industry productivity with the effects of truck travel on safety, traffic operations, and highway condition. State Regulations State governments have regulated motor vehicle dimensions since the early 1900s. Pennsylvania, in 1913, was the first state to legislate a state- wide vehicle size restriction, a width limit of 90 in. (State Limitations of Sizes and Weights 1940). By 1923 only 19 states had not adopted restric- tions on any dimension of commercial vehicles; the dimensions that were regulated included vehicle height, width, overall length, unit length, and number of units (Highway Requirements for Freight Movement 1988, 1). Width restrictions were the most common form of early state size regulation and remained the most uniform at 96 in. between 1923 and 1982 (Highway Requirements for Freight Movement 1988, 1). By the 1930s, however, the majority of states had also established regulations restricting vehicle length and height, but there was considerably more variation in these restrictions than in the width limits. The most common overall tractor-semitrailer length restriction was 45 ft, but the range extended to 60 ft (Highway Requirements for Freight Movement 1988, 2). After World War II, length limits were raised, and, by 1958, the beginning of the construction of the Interstate highway system, the most common overall length limit for tractor-semitrailers (in 28 states and the District of Columbia) was 50 ft (Four Wheel Drive Auto Co. 1958). The Arab oil embargo of 1973 resulted in another round of regulatory increases in truck size. Many states allowed the use of longer tractor- semitrailers and multiple-trailer vehicles to encourage fewer truck trips and reduce fuel consumption. By 1982 nearly 70 percent of the states allowed vehicles of the dimensions authorized by the STAA to operate on at least some roads, although many states had imposed added restrictions on overall vehicle length (TRB 1986, 24, 26). Federal Regulations The Federal-Aid Highway Act of 1956, which authorized financing and construction of the Interstate highway system, also introduced the first federal limits on truck size and weight. The regulations applied only to vehicles traveling on the Interstate system, and the purpose of the regula-
Overview17 tions, particularly those related to vehicle weight, was to protect the federal investment in the Interstate system. The only size restriction established by the act was a maximum vehicle width of 96 in.; limits on vehicle length, height, and number of trailers were not enacted. The width limit was permissive; that is, states could enforce lower limits on the Interstates if they so elected and maintain higher limits if these limits were in effect at the time the federal law was passed. States could adopt any limits they chose on non-Interstate highways. With the exception of a minor revision in federal width limits in 1976, to allow buses as much as 102 in. wide on Interstate highways, federal size regulations remained unchanged until the 1982 STAA. 1982 STAA The 1982 STAA substantially expanded federal regulation of both vehicle size and weight. The federal government preempted more restrictive state vehicle size and weight limits by establishing minimum size and weight standards, defined for the first time a network of designated highways on which STAA vehicles could travel, and made provision for access by these vehicles from this designated network to terminals and other destinations. Appendix B contains excerpts of the act related to truck size regulations. Size Provisions Federal size regulations were extended to include two new dimensions: trailer length and number of trailers; minimum rather than maximum limits were established. Trailer length: The act specifically prohibited states from limiting the length of the semitrailer in a tractor-semitrailer combination to less than 48 ft, or of each trailer in a combination vehicle with two trailers (i.e., twin trailers) to less than 28 ft on specified highways [Section 411(a)].3 Number of trailers: The act specified that states could not prohibit the use of twin trailer trucks on highways designated for vehicles of the dimensions authorized therein [Section 411(c)]. Overall combination vehicle length: The act prohibited states from enacting any overall length limit on tractor-semitrailers or on twin trailer trucks. This provision stemmed from congressional concern that overall length limits encourage reduction in truck cab size to unsafe dimensions to maximize payload capacity (U.S. Senate Report No. 97-298 1981, 3).
18 PRovIDING ACCESS FOR LARGE TRUCKS Because a truck's trailer units account for most of its length, eliminating an overall length limit, it was argued, would not substantially increase the size of the vehicle. Grandfathered length limits: The act required states to continue to allow trailers of such dimensions as were actually and lawfully being operated before its passage [Section 411(b)]. Twenty-five states had allowed semitrailer lengths of between 50 and 59.5 ft (Federal Register 1988a, 2,599). Vehicle width: Existing federal limits on truck width were liber- alized. States were required to adopt the new federal standard of 102 in. on designated highways with 12-ft traffic lanes [Section 416(a)].5 The rationale for extending the federal roie in vehicle size regulation was to improve carrier productivity by liberalizing restrictive state limits and creating more uniform national minimum standards (U.S. Senate Report No. 97-298 1981, 2). Clearly, the area of greatest variation was vehicle length. As a congressional report pointed out, "State regulations vary from a prohibition of trucks over 55 feet in overall length, to the authorization of trucks in some States on designated highways of up to 108 feet" (U.S. Senate Report No. 97-298 1981,2). The 1982 STAA achieved its goal of raising minimum standards. However, truck lengths and config- urations continue to vary widely from state to state because of the STAA grandfather provisions. National Network and Access Provisions The 1982 STAA extended federal regulatory authority over vehicle size to roads other than Interstate highways. The act specifically stated that the U.S. Secretary of Transportation was to designate a network of highways (i.e., the National Network) that would include, in addition to the Inter- state system, other segments of the Federal-Aid primary system that could safely accommodate the vehicles allowed by the act [Section 411(e)]6 The act also required states to provide reasonable access for STAA vehicles from this National Network to terminals and facilities for food, fuel, repairs, and rest (service facilities) (Section 412). Household goods carriers were allowed to travel to points of loading and unloading in addition to terminals and service facilities. The house report, which accompanied the 1982 STAA (U.S. House of Representatives Report No. 97-555 1982, 29), further elaborated that, in providing reasonable access, it was not the intent of Congress "to preempt a State's reasonable exercise of its police powers with respect to safeguarding public safety on roads
Overview 19 within the area of its jurisdiction." In the regulations that implemented the STAA [U.S. Department of Transportation (DOT) 1984, Section 658.191, the Federal Highway Administration (FHWA) chose to define neither "reasonable access" nor "terminal." The regulations simply re- quired states to make their policies available to commercial motor vehicle operators. Tandem Truck Safety Act of 1984 As implementation of the 1982 STAA proceeded, trucking industry rep- resentatives testified that nonuniformity of access policies among the states had become a considerable burden to carriers and shippers. How- ever, the Tandem Truck Safety Act of 1984 did not resolve these concerns by providing a uniform definition of reasonable access as industry had recommended. The act did clarify and revise certain provisions of the 1982 STAA regarding access and the National Network (Appendix B, Section 412). The Tandem Truck Safety Act of 1984 required that states allow travel to points of loading and unloading for single 28-ft-long by 102-in.-wide trailers (pups) used in local pickup and delivery service. Although the 1982 STAA had authorized the use of, and required reasonable access for, twin trailer trucks, it was unclear whether these provisions extended to the trailer used singly in local delivery operations. Because trucking companies prefer to use the same standard equipment for local service and for over-the-road operations to avoid rehandling freight at terminals, and because the smaller, although slightly wider,7 single trailer could replace the somewhat longer trucks then used for local delivery opera- tions, Congress believed that the smaller vehicle would not only meet the productivity concerns of the industry but would also provide an oppor- tunity for safer travel and improve local traffic conditions (U.S. Senate Report No. 98-505 1984, 4). The act also amended the original provisions of the 1982 STAA regard- ing vehicle widths (Section 416), dropping the restriction that 102-in.- wide vehicles may only be operated on those segments of the National Network with 12-ft lane widths. Instead, the act required the Secretary of Transportation to designate those portions of the National Network on which 102-in.-wide vehicles could operate safely. The committee report (U.S. Senate Report No. 98-505 1984, 14, 15) that accompanied the legislation cautioned, however, that "the safety of motorists should be the paramount concern of the Secretary in designating highways for use by 102-inch wide vehicles" and that the "Secretary should err on the side of
20 PROVIDING ACCESS FOR LARGE TRUCKS caution in designating highways." Thus revisions of the width and access provisions were intended to improve the productivity of trucking opera- tions but not at the expense of safety. The Tandem Truck Safety Act of 1984 also provided a mechanism for states to request the U.S. Secretary of Transportation to exempt from the National Network segments of the Interstate system that they deemed incapable of safely accommodating the longer and wider vehicles allowed by the 1982 STAA. Although this provision gave the states a greater role in defining the National Network, the Secretary of Transportation was not to grant any exemptions without consulting with the governors of neigh- boring states that might be affected and without examining alternative routes that could safely accommodate these vehicles. The Surface Transportation and Uniform Relocation Assistance Act of 1987 made no further amendments to provisions regarding truck access or the National Network, with the exception of the request for the present study. IMPLEMENTATION OF ACCESS PROVISIONS OF THE STAA The FHWA issued the final rules implementing the major size and weight provisions of the 1982 STAA, including access, on June 5, 1984 (U.S. DOT 1984, Title 23, Part 658). By 1985 all states but one had enacted some form of access policy, although the extent of access provided motor carriers varied widely from state to state (TRB 1986, 245). Industry Reaction At the time the rules were issued, the trucking industry raised concerns about the restrictiveness of certain state access policies and questioned whether the FHWA should define both "reasonable access" and "termi- nals" (Federal Register 1987, 299). In the FHWA's judgment, variation in local conditions precluded any single federal definition. However, the FHWA announced that it would monitor states' reasonable access policies and seek court action in states in which the intent of the law had been violated. In the fall of 1986 the National Industrial Transportation League, an organization that represents shippers, petitioned the FHWA to amend its regulations on reasonable access. Specifically, it proposed adoption of an interim rule that would (a) limit states' denial of access to posted roads
Overview 21 from which large commercial vehicles are generally excluded, to roads with lane widths less than 10 ft for 102-in.-wide vehicles, and to posted roads for which a safer alternative exists and (b) define "terminal" broadly as "any industrial, commercial, or job site location used for origination or termination" (Federal Register 1987, 299). The FHWA did not adopt the proposed rule but requested comments on reasonable access policies and practices in an advance notice of pro- posed rulemaking issued on January 5, 1987 (Federal Register 1987, 298-300). More than 200 comments were received, the preponderance from industry. More than 90 percent of carriers and shippers indicated their desire for a greater federal role in defining access (Federal Register 1988b, 33,007). Twenty state highway and transportation departments, primarily of states that restrict access, responded, and the vast majority opposed further federal involvement. The FHWA then issued a notice of proposed rulemaking that defined "terminal" and proposed national minimum access requirements of 5 mi from the National Network plus state procedures for granting access beyond the 5-mi limit (Federal Regis- ter 1988b). The Conference Report on the Continuing Resolution of December 1987 (U.S. House of Representatives Report No. 100-498), however, directed the FHWA to refrain from issuing a final rule until the present study on reasonable access was completed. Litigation The trucking industry has sought federal regulation to achieve greater uniformity of access provided by state and local governments and has initiated litigation in several states in which access policies are perceived as particularly restrictive. Central to the issue of federal regulation of access policy is the authority of the federal government to preempt the states' right to exercise their police powers to safeguard public safety. The preemption issue was at the heart of a major lawsuit on the access question brought by Consolidated Freightways [Consolidated Freightways v. Larson, 647 F. Supp. 1479 (M.D. Pa. 1986)]. The court ruled that the 1982 STAA clearly preempted conflicting state laws by the provision that "no state may enact or enforce any law denying reasonable access" [49 U.S.C. Section 2312(a)]. However, the court also noted that congres- sional intent was not "to preempt a State's reasonable exercise of its police powers with respect to safeguarding public safety on roads within the area of its jurisdiction" (U.S. House of Representatives Report No. 97-555 1982, 24). In brief, the states were prohibited from denying reasonable access but were left to define what is "reasonable." The court struck down
22 PROVIDING ACCESS FOR LARGE TRUCKS Pennsylvania's access policies because it found that the state's policy of restricting access to service facilities to 0.2 mi from the National Network without considering the availability of these facilities was arbitrary and that the state's policy for approving terminal access required "an unrea- sonable amount of time pending review of route applications, and [was based on] . . . reasons other than the safety of the public" (Consoli- dated Freightways v. Larson, 1519). A related ruling concerning New York City's regulations limiting STAA vehicle traffic on the National Network and access roads states that the city's access policies were "fatally defective and preempted under [the] Surface Transportation Assistance Act by failing to provide [the] commissioner with any guidance on what criteria govern issuance of contemplated permits" [NYState Motor Truck Ass'n v. City of New York, 654 F. Supp. 1521, 1523 (S.D.N.Y. 1987)]. Finally, a federal district court in Virginia, which overruled that state's restrictions on the use of single pup trailer units to access points of loading and unloading, found that, although the state has legitimate concern over the safety of 102-in.-wide vehicles on roads with travel lanes of 9 ft or less, these vehicles were excluded from significant miles of other state high- ways without adequate safety justification [ABF Freight System, Inc. v. Robert L. Suthard, No. 88-0018-R (E.D. Va., filed March 16, 1988), 25]. The ruling reiterated the Pennsylvania court decision that denial of access must be based on safety reasons alone and be related to the safety or operating performance of STAA vehicles on specific access roads (Con- solidated Freightways v. Larson, 1492). In summary, the courts have affirmed the right of state and local governments to exercise authority over safety matters related to access, but in so doing they must define reasonable criteria and procedures and apply them in a consistent and timely manner. CHARACTERISTICS OF AND EXPERIENCE WITH STAA VEHICLES The term "STAA vehicles" may connote greater uniformity of vehicle dimensions than was actually achieved by the STAA. The act was signifi- cant for introducing minimum vehicle size standards8 that for the first time preempted more restrictive state limits. However, maximum legal vehicle lengths continue to vary widely from state to state, in part because the 1982 STAA requires states to allow semitrailers of lengths that were actually and lawfully in use before passage of the act. Moreover, state experience with STAA vehicles differs widely; what was a vehicle of a
Overview 23 newly authorized size in one state may have been legally operated in another state for several years. These differences among states explain much of the variation in state access policies. Figure 2-1 shows the dimensions of tractor-semitrailers and twin trailer trucks authorized by the 1982 STAA. These vehicles generally replaced the common tractor-semitrailer with a 45-ft trailer and, in states that allowed them, the slightly shorter (two 27-ft trailers) twin trailer truck. The typical STAA vehicle is also 102 in. wide, 6 in. wider than the pre- STAA truck it replaced. The majority of states had legalized trailer lengths similar to those authorized by the 1982 STAA before passage of the federal legislation. [Buses 102 in. wide were allowed on Interstates in all states by federal law.] As Figure 2-2 shows, tractor-semitrailers with 48-ft trailers and twin trailer trucks with two 27-ft trailers were allowed in most states except in the East. [Several western states, however, had placed restrictions on the I 48' minimum rcw© cxc Tractor-Semitrailer 28' to 28.5' i 28' to 28.5' Twin Trailer Truck FIGURE 2-1 Vehicle dimensions authorized by the 1982 STAA.
FIGURE 2-2 Legality of STAA vehicles before passage of 1982 STAA (TRB 1986, 26-28): top, 48-ft tractor- semitrailers; middle, 65-ft twin trailer trucks; bottom, 102-in.-wide trucks.
Overview 25 long tractor-semitrailers.] The legality of 102-in.-wide trucks was far less widespread; thus many states were required to pass legislation legalizing these vehicles subsequent to the 1982 act. As Chapter 3 indicates, states' prior experience with various vehicle configurations, particularly twin trailer trucks, is highly correlated with the extent of access now provided these vehicles. Those eastern states with the least experience with the longer tractor-semitrailers and the twin trailer trucks authorized by the 1982 STAA tend to have the most restrictive access policies. A clear intent of the 1982 STAA was to bring greater uniformity to truck size and weight regulations. The act established minimum size standards for a variety of vehicle configurations, but there continues to be a wide range of vehicle sizes, particularly different vehicle lengths, that are legal in different states. Figure 2-3 shows those states with longer grandfathered trailer lengths that range from .50 ft in Tennessee to 59.5 ft in Oklahoma and Louisiana. Three-fourths of the states with these longer grandfathered trailer lengths are located in the West and the Midwest. Six eastern statesâAlabama, Delaware, Kentucky, Mississippi, Pennsylva- nia, and Tennesseeâhave grandfathered trailer lengths, none of which exceed 53.5 ft.9 Since the 1982 STAA was enacted, several states have passed legislation to allow trailer lengths of 53 ft. Thirty-four states currently allow tractor-semitrailers with 53-ft trailers on the National Network, and legislation to authorize their use is pending in another three states (Motor Carrier Advisory Service, cited in Ponzani 1989, 49). 10 [Several states, primarily in the West, allow longer combination vehicles (LCVs)âRocky Mountain doubles, turnpike doubles, and even triplesâ but these LCVs are generally restricted to certain classes of roads.]'1 These differences in legal STAA vehicle dimensions complicate the task of developing more uniform standards for reasonable access. EFFECT OF 1982 STAAON VOLUME OF TRUCK TRAFFIC The size provisions of the 1982 STAA have also had an impact on the volume of large-truck traffic. The larger STAA vehicles can carry a given amount of freight in fewer trips than the vehicles of pre-STAA dimensions they replace. The more spacious STAA 48- and 53-ft semitrailers can carry up to 13 and 26 percent more cargo, respectively, and the STAA twin trailers can carry up to 33 percent more cargo, than the 45-ft by 96-in. trailers they replace (see Chapter 4). Shippers can reduce the number of truck trips, and hence truck miles, by up to these amounts. However, because the improved efficiency of the STAA vehicles reduces transporta- tion costs, additional truck traffic may be stimulated either by diverting
ON DAKOTA is 57.4 63.5 00 0. HAWAII FIGURE 2-3 States with grandfathered semitrailer lengths greater than 48 ft on December 31, 1982 (Federal Register 1988a, 2,599).
Overview 27 freight from rail or by generating new demand for truck transportation services. The diversion from rail that can be attributed to the size provisions of the 1982 STAA is likely to be small. The productivity benefits of the larger STAA equipment mainly affect the cost of shipping low-density commod- ities; shippers of such products can take advantage of the added capacity of the STAA tractor-semitrailers without exceeding load limits. These commodities, however, are rarely moved by rail (personal communication with Brian Vogel, Intermodal Policy Division, Association of American Railroads, March 7, 1989). The STAA twin trailer trucks, with some exceptions, are generally used to carry high-value, small-shipment gen- eral freight (see Chapter 4). Rail service provides a poor substitute for the handling speed and reliability required in the transport of these products. The railroads carry mostly low-value, high-volume shipments, such as coal, grain, and chemicals, that do not require sophisticated pickup, delivery, and handling services (TRB 1986, 103; Roberts and Fauth 1988, 332-337). The amount of newly generated traffic that can be attributed to the size provisions of the 1982 STAA is more difficult to- determine. As the efficiency of truck transport increases, the prices of products that rely on truck transportation are reduced, thereby stimulating demand for these products and their transport. However, transportation is only one of the many factors that affect the final price of and demand for manufactured products. For example, a shipper of cheap shoes, for which transportation is an important component of total costs, reported that transportation costs represent 2 percent of total product costs. [Transportation generally represents 2 to 3 percent of the total cost of packaged consumer goods (personal communication with J. P. Rakowski, Memphis State Univer- sity, March 22, 1989).] Shipping the shoes in a 53-ft semitrailer instead of a 45-ft semitrailer reduced transportation costs by one-quarter so that they now represent 1.5 percent of total product costs. Such relatively small changes in trucking costs alone should not have a major impact on demand for these products. Reduction in the cost of truck transportation may cause some manufac- turing firms to move farther from major highways to take advantage of cheap land and labor as transportation costs become a less critical part of their total production costs. This would increase the miles traveled by trucks. However, the farther they move, the more these firms erode the cost advantage. The magnitude of these effects is difficult to determine, but it is likely that changes in vehicle size, in comparison with deregula- tion of the rail and trucking industries, have had only a modest role in reducing the cost of truck transportation. Moreover, transportation costs
28 PROVIDING ACCESS FOR LARGE TRUCKS are only one of several factors that drive industry locational decisions and distribution practices. The net effect of all of the factors just discussed is likely to be a smaller increase in truck traffic than would have been experienced with equip- ment of pre-STAA dimensions. The larger STAA vehicles can carry a given amount of freight in fewer trips. The increased efficiency of the equipment, although unlikely to divert much freight from rail, may generate some new truck traffic. The net effect will be to mitigate some of the adverse impacts of truck travel on safety, traffic congestion, and pavement service life. These impacts are explored in subsequent chap- ters, but, first, an overview of current state access policies is presented to provide perspective on the nature and extent of access problems and a framework within which to analyze policy options. NOTES The Surface Transportation Assistance Act of 1982 was passed by Congress in December 1982 but was not signed into law until January 1983. The extent to which the efficiency of larger equipment is responsible for increased truck volume is not clear. Use of larger equipment will reduce the number of trips required to move a given quantity of freight. However, the improved efficiency in trucking operations may also divert additional freight from other transportation modes, thereby increasing the volume of goods carried. Because some major carriers were legally operating 28.5-ft twin trailers within the common 65-ft overall vehicle length limit, the act also prohibited states from restricting the use of existing twin trailers of this length [see Section 411(b), Appendix B]. Two states, Indiana and Rhode Island, had grandfathered trailer lengths of 48.5 ft, which were considered, for all practical purposes, equivalent to 48 ft. Hawaii was exempted from this maximum limit and its 108-in, limit allowed to stand. Highways to be included on the National Network were identified by the U.S. Secretary of Transportation in consultation with the states. An initial determina- tion of roads was to be made within 3 months, a final determination within 9 months, and the Secretary could revise the designations as necessary (TRB 1986, 50). These wider pups may still create problems on local streets with very narrow lane widths; however, their shorter length may alleviate traffic congestion. In many states, the minimum standard is also the maximum. For example, states cannot restrict tractor-semitrailers with trailer lengths less than 48 ft but trailer lengths greater than 48 ft are not legal except in those states in which semitrailer lengths greater than 48 ft were grandfathered. If they meet wheelbase restrictions, tractor-semitrailers that are longer than the legal tractor-semitrailer are allowed in California, Indiana, Michigan, Minnesota, Tennessee, and Wisconsin. These wheelbase restrictions will be discussed in more detail in Chapter 3. Rhode Island and Indiana have grandfathered trailer lengths
Overview 29 of 48.5 ft, which, for all practical purposes, were considered equivalent to the 48-ft trailer dimension. Ten of these states have imposed overall length limits or wheelbase restrictions on, or require permits for, use of these vehicles (Motor Carrier Advisory Service, cited in Ponzani 1989,49). Fifty-three-foot trailers are not legal on the National Network in the six New England states, Alaska, Hawaii, Idaho, Maryland, New Jersey, New York, West Virginia, and the District of Columbia. Legislation to allow 53-ft trailers is pending in Georgia, North Carolina, and South Carolina. Thirty-four states allow the use of 53-ft trailers off the National Network, but 24 of these states have placed restrictions on their use. A Rocky Mountain double has one tandem-axle 40- to 48-ft trailer and a second single-axle 27- to 28-ft trailer; a turnpike double has two tandem-axle 48-ft trailers; triples have three trailers. Rocky Mountain doubles are currently permitted in 11 states, triples in 6 states, and turnpike doubles in 7 statesâall western states (March 1986, 158). In addition, Florida, Indiana, Kansas, Massachusetts, New York, and Ohio allow certain of these vehicles to travel on turnpikes (March 1986, 158). REFERENCES ABBREVIATIONS FHWA Federal Highway Administration TRB Transportation Research Board U.S. DOT U.S. Department of Transportation Federal Register. 1987. Vol. 52, No. 2, Jan. 5, pp. 298-300. Federal Register. 1988a. Vol. 53, No. 19, Jan. 29, pp. 2,597-2,599. Federal Register. 1988b. Vol. 53, No. 251, Dec. 30, pp. 53,007-53,012. Four Wheel Drive Auto Co. 1958. Truck and Trailer Size and Weight Restrictions. Clintonville, Wis. Highway Requirements for Freight Movement. 1988. Working Paper 12. The Future National Highway Program: 1991 and Beyond. FHWA, U.S. Depart- ment of Transportation, Feb. March, J.W. 1986. Findings of the Longer Combination Vehicle Study. In Trans- portation Research Record 1052. TRB, National Research Council, Washing- ton, D.C., pp. 157-161. Ponzani, L. 1989. Acceptance of 53-Foot Trailers is Growing. Transport Topics, Feb. 27, p. 1. Roberts, P.O., and G.W. Fauth. 1988. The Outlook for Commercial Freight Transportation. In A Look Ahead: Year 2020. Special Report 220. TRB, National Research Council, Washington, D.C., pp. 329-353. State Limitations of Sizes and Weights. 1940. Report No. 1 in Ex Parte No. MC-15. Bureau of Motor Carriers, Interstate Commerce Commission, June. TRB. 1986. Twin Trailer Trucks. Special Report 211. National Research Council, Washington, D.C., 388 pp. U.S. DOT (FHWA). 1984. Truck Size and Weight, Route DesignationsâLength, Width and Weight Limitations. Code of Federal Regulations, Title 23, Chapter 1, Part 658, June 5.
30 PROVIDING ACCESS FOR LARGE TRUCKS U.S. House of Representatives Report No. 97-555. 1982. Committee on Public Works and Transportation. 97th Cong., 2d Sess., May 17. U.S. House of Representatives Report No. 100-498. 1987. Conference Report on House Joint Resolution 395. 100th Cong., 1st Sess., Dec. 21. U.S. Senate Report No. 97-298. 1981. Committee on Commerce, Science, and Transportation. 97th Cong., 1st Sess., Dec. 14. U.S. Senate Report No. 98-505. 1984. Committee on Commerce, Science, and Transportation. 98th Cong., 2d Sess., June 6.
3 Current Access Policies and Practices T HE SURFACE TRANSPORTATION ASSISTANCE ACT (STAA) of 1982 provided that no state could deny reasonable access to STAA-authorized vehicles between the National Net- work and terminals and facilities for food, fuel, repair, and rest (i.e., service facilities). However, it has essentially been left to state discretion to determine what constitutes "reasonable access." The final rule imple- menting the legislation stipulates that states and local governments may not restrict access without a reasonable safety-related justification and provides that the Federal Highway Administration (FHWA) will monitor state and local access policies to ensure conformity with the intent of the legislation (Federal Register 1988, 12,149). Since the final rule was promulgated in 1984, all states have established access policies, but these policies vary widely from state to state. Several states simply adopted the federally mandated minimum vehicle size limits on all state-administered roads or on all public roads, effectively provid- ing unrestricted access to all STAA vehicles. Typically, these were states in which twin trailer trucks and longer tractor-semitrailers had been in legal use before passage of the 1982 STAA. The remaining states adopted a variety of access policies, reflecting their prior experience with STAA vehicle configurations, variations in roadway types and conditions, and differences in jurisdictional authority over highways. This chapter contains the results of a review of existing access policies of state and local governments. The review was conducted to Define the extent of highways open to STAA vehicles and identify areas of the country where travel is most restricted, 31
32 PROvIDING ACCESS FOR LARGE TRUCKS Determine procedures used by state and local governments to define and implement access policies, and Identify key elements of access policies and procedures that have enabled government and industry to reach agreement on the provision of reasonable access. The information in this chapter was obtained primarily through surveys of the highway and transportation departments of all 50 states and the District of Columbia, as well as state trucking associations (Appendix C). Telephone interviews were also conducted with local highway officials representing counties, cities, and metropolitan planning organizations in 12 states. EXTENT OF HIGHWAYS OPEN TO STAA VEHICLES Nationwide, there are more than 3.8 million miles of public highways and streets (Table 3-1). Except for minor amounts of mileage, primarily on federal lands, practically all of these roads are under the jurisdiction of state and local governments. Approximately 850,000 mi, however, are constructed and maintained primarily with federal funding and are there- fore classified as Federal-Aid highways. The Federal-Aid system has three components: The Primary system, which consists of 44,000 mi of Interstate high- ways and 258,000 mi of arterial highways that connect cities and centers of economic activity;1 The Secondary system, which is composed of 398,000 mi of rural major collector roads linking farms and smaller communities with the primary system; and TABLE 3-1 U.S. ROAD MILEAGE AND TRAVEL, 1987 (Highway Statistics 1987 1988, 110, 173) System Miles Share (%) Vehicle-Miles (millions) Share (%) Federal-Aid Interstate 44,328 1 417,205 22 Other primary 258,120 7 557,869 29 Secondary 398,329 10 166,298 9 Urban 147,979 4 427,897 22 Subtotal 848,756 22 1,569,269 82 Off Federal-Aid 3,025,270 78 355,058 18 Total 3,874,026 100 1,924,327 100
Policies and Practices 33 The Urban system, which includes 148,000 mi of high traffic volume arterials and collectors in urban areas. The Federal-Aid system is composed of about 20 percent of the country's highway mileage but carries 80 percent of all traffic (Table 3-1). As stipulated by the 1982 STAA, the FHWA, in consultation with the states, has placed portions of the Federal-Aid primary (FAP) system that link major metropolitan areas and industrial centers on the National Network. To supplement this network, states have placed many other highways on state through-travel networks and approved additional miles for access to terminals and service facilities. Thus, in the subsections that follow, three categories of highways open to STAA vehicles are discussed: The National Network, which includes federally designated Inter- state highways and portions of the non-Interstate FAP system open to all STAA vehicles; Additional highways independently approved by the states for through travel by all, or some, STAA vehicles; and Access roads approved by state and local governments to connect through-travel highways with terminals and service facilities. National Network The National Network comprises approximately 183,000 mi of highways, including the 44,000-mi Interstate system2 and 139,000 mi of other FAP highways, or about three-fifths of the entire FAP system (Table 3-2). The network was devised as a compromise between limiting STAA vehicles to the Interstate system, an approach that would have severely curtailed the use of these vehicles, and permitting them on all primary highways, an TABLE 3-2 MILEAGE ON THE NATIONAL NETWORK, 1987 (Highway Statistics 1987 1988, 132) Other FAP Percentage of Total Region Interstate Miles' Miles FAP Miles West 12,400 29,900 67 Midwest 17,100 90,300 80 East 14,800 18,400 33 U.S. Total 44,300 - 138,600 60 See Figure 3-1 for definition of regions. bVirtually all Interstate highways are part of the National Network.
34 PROVIDING ACCESS FOR LARGE TRUCKS approach that would have imposed few practical limits on their use (TRB 1986, 54). The fraction of FAP mileage placed on the National Network varies greatly among states and across regions of the country, ranging from more than two-thirds in 18 states3 to less than one-third in 17 states and the District of Columbia (Figure 3-1). Except for Alaska and California, all of the states with less than one-third of their primary highways on the National Network are located in the East; in comparison, 15 of the 18 states that have more than two-thirds of their primary mileage on the National Network are located west of the Mississippi. State-Designated Through-Travel Highways In addition to the National Network, roughly 40,000 additional miles of FAP highways have been placed on state through-travel networks. Many of these highways are open to all STAA vehicles and, in effect, are equivalent to the National Network; others have additional restrictions prohibiting certain types of STAA vehicles. Highways Open to All STAA Vehicles In addition to the 18 states with extensive mileage on the National Net- work, 9 others, all in the West and Midwest, allow STAA vehicles to operate unrestricted, or with few practical restrictions, on most highways including virtually all FAP highways.4 Although many of these highways were effectively open to twin trailer trucks and large tractor-semitrailers before passage of the 1982 STAA, state officials have not added them to the National Network in order to retain final control over truck size limits. As shown in Figure 3-2, if these state-designated miles are added to the mileage on the National Network, the number of states with more than two-thirds of their primary highways open to STAA vehicles increases from 18 to 27, and the percentage of FAP miles open nationwide increases to approximately 70 percent. Highways Open to Some STAA Vehicles Several other states allow some types of STAA vehicles, but limit others, on large portions of their primary systems. There limits often reflect the individual state's experience with particular vehicle configurations before
West Midwest East i L CflOflU0 Less than one-third - One-third to two-thirds Two-thirds to all AWfl,, FIGURE 3-1 Share of Federal-Aid primary mileage on the National Network.
West Midwest East 1 /1 El I IScOcT L / co Cb f 0/ 4LA0 4 Tco-thdS to all FIGURE 3-2 Share of Federal-Aid primary mileage open to all STAA vehicles (including mileage on the National Network and state-designated networks).
Policies and Practices 37 enactment of the 1982 STAA' and concerns about the ability of the highway systems to safely accommodate these vehicles. Typical restrictions include Bans on multitrailer trucks: In virtually all eastern states where twin trailer trucks were prohibited before passage of the 1982 STAA, few highways, apart from those already on the National Network, have been opened to twins. In most cases, these states have retained pre-STAA prohibitions on multitrailer trucks on highways off the National Network, restricting travel to specific terminal access routes or prescribed distances from the National Network. (These access provisions are discussed in more detail in following sections.) Length limits: State limits on truck and trailer lengths also prevent many STAA vehicles from operating on highways off the National Net- work. For example, several states (e.g., Massachusetts, New York, North Carolina, and Virginia) have retained 45-ft trailer length limits on non- Network roads; others (e.g., South Carolina, Vermont, and West Vir- ginia) have adopted 60-ft overall length limits that restrict the operation of both twins and tractor-semitrailers. Width limits: A few, primarily eastern, states continue to restrict 102-in.-wide trucks; however, these limits are often liberally applied, and thus their practical restrictive impact on STAA vehicles is minimal. For example, New Jersey has designated a 4,000-mi supplemental network, which is composed of virtually all primary highways and many secondary roads, for use by wider trucks. Alabama, Florida, and New Hampshire now permit 102-in.-wide tractor-semitrailers on highways with 12-ft lanes, which include more than 80 percent of the primary highways in these states. Wheelbase limits: A number of states, mostly in the West and the Midwest, regulate the wheelbase dimension of STAA semitrailers, typ- ically measured from the kingpin (the vertical pin under the front end of a semitrailer that fits into the tractor to couple the two units together) to the rear trailer axle or axles. These limits are intended to improve the maneu- verability of longer tractor-semitrailers.6 Nine statesâCalifornia, Idaho, Illinois, Iowa, Maiiié,:Michigan, Minnesota, Tennessee, and Wisconsinâ regulate the wheelbase distances of STAA vehicles traveling off the National Network (Table 3-3). In practice, the regulation of twins tends to be more restrictive than that of tractor-semitrailers.7 As shown in Figure 3-3, twins are confined to less than one-third of FAP mileage in 16 states and the District of Columbia, whereas only 9 states and the District of Columbia similarly restrict STAA tractor-semitrailers. Several eastern states that impose few practical limits
38 Piov1DING ACCESS FOR LARGE TRUCKS TABLE 3-3 STATES WITH WHEELBASE LIMITS Distance from Kingpin to State Rear Axle (ft) California 40 Idaho 39 Illinois 40 Iowa 40 Maine 38 Michigan 40.5 Minnesota 41 Tennessee 41 Wisconsin 41 Nom: The wheelbase distance is typically measured from the kingpin setting to the rear trailer axle or axles; although in Maine it is measured from the rear tractor axle instead of the kingpin. Not included in this table are Utah, which has a 40.5-ft kingpin- to-rear-axle limit for trailers longer than 48 ft (its legal STAA trailer length), and Indiana, which allows trailers up to 53 ft long if the distance from the kingpin to the rear trailer axle or axles does not exceed 40.5 ft but does not regulate the wheelbase distance of its STAA-grandfathered 48.5-ft trailer. See Appendix C, Table C-3, for more details. on STAA tractor-semitrailers (Alabama, Connecticut, Florida, Maine, New Jersey, and Rhode Island) severely limit the operation of twins. Thus, in the East, roughly one-third of the primary system is open to twin trailer trucks whereas one-half is open to STAA tractor-semitrailers. Nationwide, twins are allowed on 70 percent of all primary highways; 75 percent of these highways is open to STAA tractor-semitrailers (Table 3-4). Access Roads The final category of roads open to STAA vehicles is those providing access between through-travel highways and terminals and service facili- ties. Describing the extent and condition of these roads, however, is difficult because in many states they include thousands of short road segments. The majority of state highway and transportation departments interviewed for this study were unable to provide estimates of mileage or type of access roads. In general, states in the Midwest, and the few western states that regulate access, have access mileage limits of 5 mi or more. Because these states have already placed a large share of their highways on through- travel networks, many local streets and roads fall within these distances and, for all practical purposes, STAA vehicles are allowed on virtually all
East Midwest West S wSCONS 'O4M0 OJtOAKOA Ic- .a'"° cOt 0 V W. IIi aaf en with dilough-travot States with tirrled ttrrough-tcavoI snienqo for both twins and tractor- somwaitcrs FIGURE 3-3 States with limited (less than one-third of Federal-Aid primary) through-travel mileage for STAA vehicles.
40 PROVIDING ACCESS FOR LARGE TRUCKS TABLE 3-4 PERCENTAGE OF FAP MILEAGE OPEN TO STAA VEHICLES BY VEHICLE CONFIGURATION Percentage Open Percentage Open to STAA Region to Twins Tractor-Semitrailers West 93 93 Midwest 91 91 East 35 48 U.S. Total 70 75 NcYrE: See Appendix C, Table C-i, for more details public roads. In comparison, eastern states tend to provide short dis- tances (0.2 to 3 mi) for access to terminals and service facilities within close proximity to the National Network; access beyond these distances is usually provided after a route evaluation, and approved routes seldom exceed 5 mi in length. Because these states also have limited through- travel mileage, access routes are often composed of arterial and collector highways connecting with the National Network and are less likely to include local roads and streets. In some cases, access roads significantly expand the amount of mileage open to STAA vehicles, especially in states that have limited through- travel mileage. Examples of states that lack significant through-travel mileage, but have broadly defined access, include Maryland and Tennes- see, where carriers are allowed to use their own discretion to choose the "shortest practical route" to terminals, and several states in the West and the Midwest (e.g., Alaska, Missouri, and New Mexico) that allow STAA vehicles to travel a substantial distance (10 to 25 mi) from the National Network and state-designated highways. As is observed in the following subsections, many of the states at the center of the debate over truck access have both minimal through-travel and minimal access mileage. Thirteen states, all in the East (Alabama, Connecticut, Florida, Georgia, Maine, Massachusetts, New Jersey, New Hampshire, New York, Pennsylvania, Rhode Island, Vermont, and West Virginia), and the District of Columbia appear to fit this description; each has opened less than one-third of its FAP mileage to STAA vehicles and typically limits terminal accessto within 5 mi of the National Network. Reasons for Restricting Travel In response to the survey, the principal reasons given by states for limiting the operation of STAA vehicles included
Policies and Practices 41 STAA-authorized truck size limits are too high given the physical characteristics of many roadways. Twins were the major concern in the East where they had not been common, but several states also noted that longer tractor-semitrailers are a problem. Eastern states, in particular, reported that many of the curves and intersections in their systems were designed to accommodate much smaller vehicles and that they feared safety problems as a result of the longer trucks. Also, several states reported that large portions of their highway systems contained roads with lanes less than 12 ft wide or alignments difficult for wider vehicles to negotiate. The larger STAA vehicles would adversely affect highway traffic operations. Several states expressed concern that their highways might be limited in their ability to efficiently handle large-truck traffic, noting that many urban roads, in particular, are sensitive to increases in truck sizes because of their high traffic levels and the number and width of lanes. More generally, states objected to the scope of federal preemption of their authority over truck size limits, claiming that states are in the best position to judge the adequacy of their highway systems to accommodate STAA vehicles, and that each state system has its own peculiarities that make nationally uniform truck size limits impractical. Regional Variation in Highway Characteristics Available data on the physical and use characteristics of Federal-Aid highways suggest that, as indicated by the states, highway conditions can be highly diverse. Data collected by the FHWA reveal the following kinds of regional differences: Lane width: As the data in Table 3-5 indicate, lane widths are generally narrowest in the East. The eastern states have a higher percent- age of lanes that are 10 ft or less wide than do other regions of the country. Roughly 20 percent of non-Interstate FAP highways8 in the East have lanes that are 10 ft or less wide, compared with about 10 percent in the Midwest and the West. Nearly half of the non-Interstate Federal-Aid system in the East has lanes 10 ft or less wide, which is about double the percentage of the other regions. Urban mileage: Figure 3-4 provides a comparison by region of the share of non-Interstate Federal-Aid highways located in urban areas. As might be expected, eastern highways tend to be located in and around cities more often than do western and midwestern highways. In the East, about 30 percent of Federal-Aid highways is located in urban areas, compared with about 16 percent in the Midwest and 25 percent in the West.
42 PROVIDING ACCESS FOR LARGE TRUCKS TABLE 3-5 PERCENTAGE OF NON-INTERSTATE FEDERAL-AID MILEAGE BY LANE WIDTH (Highway Statistics 1987 1988, 120-121) Region and Lane Width (ft) Federal-Aid System Primary Secondary Urban Total West :510 9 24 23 18 11 14 16 13 15 a:12 77 60 64 67 100 100 100 100 Midwest 10 8 41 13 28 11 15 23 19 20 a~12 77 36 48 52 100 100 100 100 East 10 21 70 38 44 11 20 21 15 19 -12 59 9 47 37 100 100 100 100 U.S. Total 10 13 47 27 32 11 16 22 16 19 12 71 31 57 49 100 100 100 100 Traffic volumes: Reflecting the high population densities of many eastern states, traffic volumes are notably higher in the East than in the rest of the country. As shown in Figure 3-5, average daily traffic volumes on about 40 percent of PAP (non-Interstate) highways9 in the East exceed 5,000 vehicles per day, which is roughly double the share of primary highways with similar volumes in the Midwest and the West. The relationship between these variations in Federal-Aid highway con- ditions and the uneven distribution of through-travel and access mileage across geographic regions, however, is not clear. The truck sizes permitted by the STAA constituted a much more drastic alteration of existing limits in the East than in other parts of the country where twin trailer trucks and longer tractor-semitrailers had been common for many years. Differences among states in familiarity and experience with STAA vehicles have no doubt also played an important role in some states' decisions to tightly regulate these vehicles.
35 LU 30 25 LL 0 20 ul 15 OC 10 w C- 5 0 West Midwest East FIGURE 3-4 Federal-Aid (non-Interstate) mileage located in urban areas (Highway Statistics 1987 1988, 116). 100 Uj 80 60 LL LU Lu :: 0 80% 77% 58y J30% J West Midwest East ADT 15,000 or more M ADT 5,000 to 14,999 ⢠ADT Less than 5,000 FIGURE 3-5 Federal-Aid primary (non-Interstate) mileage classified by average daily traffic (ADT) volume (Highway Statistics 1987 1988, 125-126).
44 PROVIDING ACCESS FOR LARGE TRUCKS Summary Assessment Nationwide, approximately 70 percent of FAP system mileage is effec- tively open to all STAA vehicles. However, there are sharp regional differences. STAA vehicles are virtually unrestrained in the West as well as in many midwestern states that have placed a large share of their primary highways on the National Network or on state-designated net- works. The states that res'trict STAA vehicles the most are in the East, where highway officials are concerned that many roads are unsuitable for larger trucks and where many STAA vehicles were illegal before the 1982 STAA. As a group, eastern states allow twin trailer trucks on approx- imately one-third, and tractor-semitrailers on approximately one-half, of their primary highways. Access roads to terminals and service facilities have significantly ex- panded the amount of mileage open to STAA vehicles in those eastern states that have limited through-travel networks but liberal access provi- sions. Disputes over truck access are most heated in eastern states that have limited both through-travel networks and access roads. STATE ACCESS PROVISIONS Access is not an issue in the 15 states that effectively allow STAA vehicles on all public roads.1° The remaining 35 states and the District of Colum- bia have adopted a broad range of access rules, route restrictions, and administrative procedures that complicate the task of defining access policies and practices. Responses to surveys of state highway and transportation departments and trucking associations revealed important state-to-state differences in the following areas: Definitions of "terminal," Procedures for providing access, and Implementation of access provisions. Definitions of "Terminal" Neither the STAA nor its implementing regulations define the word "terminal" as it relates to reasonable access. However, about one-third of
Policies and Practices 45 the states and the District of Columbia have defined the term in legislation or regulations. Wording that has been adopted by a number of states specifies that STAA vehicles can access all "points of loading and unloading." How- ever, concerned that such a broad definition would result in STAA vehi- cles servicing businesses located in congested downtowns, 10 states have defined "terminal" in such a way as to specifically exclude retail stores and other businesses that are often located in congested business districts (Table 3-6). Many of these definitions are based on the traditional concept TABLE 3-6 STATES WITH FORMAL DEFINITIONS OF TERMINAL Staten Qualifying Destinations Effective Limitations Alabama Truck terminals and dis- Applied to twins only tribution centers California Businesses where full Interpreted to include vir- truckloads can be tually all points of load- loaded and unloaded ing and unloading; the adequacy of the route is emphasized Florida Truck terminals and dis- Applied to twins only tribution centers Georgia Truck terminals and dis- Interpreted to include vir- tribution centers tually all points of load- ing and unloading Maine Truck terminals and dis- Applied to twins only tribution centers Massachusetts Truck terminals and dis- Prohibits access to some tribution centers retail stores and manu- facturing facilities' New Hampshire Truck terminals and dis- Applied to twins only tribution centers New Jersey Truck terminals and dis- Applied to twins only tribution centers New York Truck terminals and man- Prohibits access to retail ufacturing and ware- stores house facilities Pennsylvania Locations with adequate Interpreted to include vir- off-roadway space for tually all points of load- vehicle maneuvering ing and unloading °States that have defined terminal in statutes or regulations, excluding states that have broadly defined terminal as a "point of loading and unloading." bTerminal definition does not apply to businessesâincluding retailers and manufac- turersâlocated within 1.5 mi of the National Network.
46 PROVIDING ACCESS FOR LARGE TRUCKS of a truck terminal, that is, a location with a minimum number of loading stations that is used primarily to transfer freight to smaller vehicles for local pickup and delivery. Judging from the responses to surveys of state trucking associations, the definitions of "terminal" have caused surprisingly few problems for users of STAA vehicles. There appear to be two main reasons for this. First, many states place greater emphasis on the adequaà y of the roadway than on strict interpretations of the definitions. For example, highway officials in California, Georgia, and Pennsylvania reported that present practice in their states is to evaluate all requests for access, regardless of whether the trucking destination meets the state's formal definition. Second, state definitions of "terminal" are often compatible with the needs of users of STAA vehicles. For example, restrictive terminal defini- tions often apply only to twin trailer trucks, which are used primarily by the small-shipment (less-than-truckload) segment of the trucking indus- try for line-haul operations between large truck terminals, which meet these more restrictive definitions." Definitions of "terminal" can create problems in the few statesâ California, Georgia, Massachusetts, New York, and Pennsylvaniaâin which they apply to STAA tractor-semitrailers as well as to twin trailer trucks. Unlike twins, tractor-semitrailers are used by a wide variety of carriers and shippers who move freight between numerous locations (e.g., grocery stores, warehouses, manufacturing facilities, and construc- tion sites) that seldom qualify as truck terminals according to more restrictive definitions. Procedures for Providing Access As the data in Table 3-7 indicate, most states use one or both of the following procedures for providing access: (a) a distance-based approach that allows STAA vehicles to travel on any road within a specified number of miles from the National Network or other state-designated highways or (b) a route-designation procedure for examining the adequacy of the roadway to accommodate STAA vehicles, typically in response to re- quests from carriers and shippers. The first approach offers the advantage of being simple to implement and easy to enforce, and the latter approach allows states to evaluate and monitor the roads open to STAA vehicles. Distance-Based Access Fourteen states have adopted specific mileage limits as their primary method of providing access (Table 3-8). These limits are most common in
Policies and Practices 47 the Midwest and the West, where many states have placed large portions of their highway systems on the National Network or on extensive state networks. For example, Illinois, Iowa, and Michigan have adopted a 5-mi limit from the National Network and other state-designated highways. Each of these states has opened more than 75 percent of its primary highway system to STAA vehicles in addition to large portions of its secondary and urban system roads. In comparison, in eastern states distance limits tend to be short and coupled with limited through-travel mileage. For example, operators of STAA vehicles can travel 1 to 3 mi from the National Network for access in Alabama (twins only), South Carolina, and West Virginia, but in each of these states less than one-third of FAP highways is on the National Network. Access Route Designation Nineteen states and the District of Columbia grant terminal access to some STAA vehicles through a route-designation procedure whereby all routes open to STAA vehicles are evaluated and approved by state officials. Seven of these statesâArizona, California, Georgia, Minnesota, North Dakota, Oregon, and Utahâhave reviewed large portions of their highway systems to provide additional through-travel and access mileage. Of these seven states, Georgia has opened the fewest miles, about 350 mi for twins, and California has been the most active, having reviewed the entire state highway system and opened more than 5,000 mi to STAA vehicles since 1983. Twelve states, all in the East, and the District of Columbia review access routes on request. Nine of these states and the District of Columbia grant access by permit; three statesâNew York, Pennsylvania, and Vir- giniaâopen approved access routes to all carriers. In general, the access roads in these 12 states are short and composed of many road segments (averaging less than 3 mi) that lead to specific terminals and seldom connect at both ends with the National Network. The states with the most active application programs are Florida, Massachusetts, New York, Pennsylvania, and Virginia. Together, these five states have received more than 2,000 requests for access, and each has reviewed more than 200 applications. Only one state, Vermont, has rejected more than half of its requests, whereas Connecticut and New Jersey have approved more than 90 percent. Other states reported ap- proval rates of between 60 and 80 percent. Obtaining access permission typically takes 30 to 45 days. Connecticut reported the shortest review period, 2 weeks; Florida indicated that, in
TABLE 3-7 SUMMARY OF STATE ACCESS PROCEDURES Region Procedure West Midwest East Unlimited access (19) Colorado Arkansas Connecticut" Hawaii Indiana Maine" IdahoL Kansas Mississippi Montana Nebraska Rhode Island" Nevada Ohio Washington Oklahoma Wyoming South Dakota Texas Mileage limit (14) Off National Network Alaska Louisiana Kentucky' Missouri North Carolina South Carolina Off National Network and New Mexico Illinois Alabama" state-designated network Iowa New Jersey" Michigan West Virginia Wisconsin
Route designation (20) State-designated network Arizona California Oregon Utah On request Other (6) Idaho Nore: See Appendix C, Tables C-2 and C-3, for details. Applies to tractor-semitrailers only. bApplies to twins only. cShort mileage limits may apply, primarily for access to services. Minnesota Georgia North Dakota Connecticutb Delaware D.C. Floridab Maineb Massachusetts New Hampshireb New Jersey" New York Pennsylvania Rhode Island" Vermont Virginia Alabama Florida' Maryland New Hampshire Tennessee
50 PROVIDING ACCESS FOR LARGE TRUCKS TABLE 3-8 SUMMARY OF STATES WITH DISTANCE-BASED TERMINAL ACCESS POLICIES Percentage of Distance PAP Mileage Region and State Limit (mi) Open to STAA Vehicles West Alaska 25 23 New Mexico 20 >80 Midwest Illinois 5 92 Iowa 5 >80 Louisiana 3 100 Michigan 5 77 Missouri 10 45 Wisconsin 5 62 East Alabama 1 30 Kentucky 5 51 New Jerseyb 2 >90 North Carolina 3 60 South Carolina 3 29 West Virginia 2 25 Nom: Distance also applies for access to service facilities. See Appendix C, Tables C-2 and C-3, for more details. Applies to twins only. bApplies to tractor-semitrailers only. extreme cases, reviews can take 2 months or longer. Three statesâ Delaware, Maine, and Vermontâand the District of Columbia grant access for a limited time only-,'access routes in other states, once ap- proved, are open indefinitely. Commonly used criteria for reviewing routes include length of the route, number and width of travel lanes, roadway geometry, accident history of the route, traffic volume and composition, and abutting land uses (e.g., residential, commercial, school). Thirteen of these states allow STAA vehicles to travel short distances (usually ito 3 mi) from the National Network for the primary purpose of reaching service facilities (Table 3-9). Three of these statesâFlorida, Maine, and Rhode Islandâauthorize longer distances in rural areas, and two states, California and Vermont, indicate with signs where STAA vehicles can travel 0.5 mi to service facilities.
Pblicies and Practices 51 TABLE 3-9 SUMMARY OF STATES WITH DISTANCE LIMITS FOR ACCESS TO SERWCE FACILITIES Percentage of Distance FAP Mileage Region and State Limit (mi) Open to STAA Vehicles West California' 0.5 >70 Oregon 0.5 >80 East Connecticut" 0.5 29 Florida" ito 3 18 Maine" 0.5 to 2 16 Maryland 1 30 New Jersey 27 >90 New York 1,500 ft 26 Pennsylvania 0.2 19 Rhode Island" 1 to 3 19 Vermont 0.5 24 Virginia 0.5 40 West Virginia 2 25 NOTE: In some states these distance limits may also be used for access to terminals located near the National Network. Florida, Maine, and Rhode Island have adopted longer distance limits for rural highways (see Appendix C, Tables C-2 and C-3, for more detail). Applies to twins longer than 75 ft and tractor-semitrailers longer than 65 ft orwith wheelbase dimensions exceeding 40 ft, measured from the kingpin to the rear trailer axles. bApplies to twins only. "Applies to tractor-semitrailers only. Other Procedures Six states have developed access policies that are notably different from those just described. Maryland and Tennessee allow carriers to choose the "shortest practical route" to terminals; truck operators are expected to stay on the National Network for as long as practical before exiting for access. (Maryland, however, has adopted a 1-mi distance limit for access to service facilities.) Alabama, Florida, and New Hampshire limit STAA tractor-semitrailers to highways with 12-ft lanes, and Idaho has closed about 1,000 mi of highways to tractor-semitrailers that exceed minimum wheelbase limits. (Idaho is unlike other states in that it designates routes that are closed, rather than open, to STAA vehicles).
52 PROVIDING ACCESS FOR LARGE TRUCKS Implementation To determine how state access provisions are implemented, state highway officials and trucking associations were asked to describe how carriers are informed of access regulations, how conflicts are resolved, and how these regulations are enforced. Information and Conflict Resolution The following methods are used to provide information on access: Truckers' handbooks are published and distributed by many states to truckers as a reference to state laws and regulations pertaining to truck- ing, including access regulations. In states with complex access-permit- ting provisions, these books are useful for providing a list of agencies to contact for access permission, but they seldom provide maps or lists of specific access routes and often fall short of fully and clearly explaining access regulations. Maps are usually published by states with large truck networks to show through-travel highways, such as the National Network and other state-designated highways. However, maps are rarely used to show termi- nal access routes because these routes tend to be short, often are open only to the applicant, and frequently must be revised as additional access roads are approved. Uniform signs, which have been adopted by the Manual on Uniform Traffic Control Devices and incorporated in the final rule implementing the provisions of the 1982 STAA (U.S. DOT 1984, Title 23, Part 658, 267), are used by a number of states to identify highways on the National Network. These signs, however, pertain only to the National Network, and their use by the states is voluntary. Only two statesâCalifornia and Vermontâuse signs to identify specific access roads.12 States with mileage limits on access report that signing would be impractical and prohibitively expensive because of the many thousands of short road segments that fall within these distance limits. In states that grant access through permitting procedures, access routes are rarely signed and typically are identified to individual permit holders only. Published lists are usually issued to carriers by states that grant access by permit. In most cases, these lists are sufficient because permit holders are already familiar with approved routes. However, carriers find lists cumbersome and impractical as a means of identifying access routes open to all STAA vehicles.
Policies and Practices 53 Motor carrier advisory groups, in response to the growing concern of the trucking industry about the complexities of access policies, provide a formal mechanism for the trucking industry to work with state officials to resolve access problems. Trucking associations in at least two states with a history of controversy over the extent of access providedâAlabama and Pennsylvaniaâreported noticeable improvements in the resolution of access problems after meetings of these groups. Enforcement The level of enforcement of access regulations varies widely from state to state. As might be expected, states with substantial through-travel net- works and access mileage reported the fewest problems enforcing access regulations; most reported that fewer than 10 citations are issued per month for access violations. Enforcement appears to be more stringent in the East, where access is most limited. State officials and trucking associations in Georgia, New York, Pennsylvania, and Virginia reported the highest number of tickets issued per month, largely because these states limit access to both twins and STAA tractor-semitrailers. In comparison, states that restrict only twins reported fewer access violations, noting that these vehicles usually operate among a small number of terminals over well-defined routes and are easily recognized by enforcement officials, which is, perhaps, a deter- rent to carrier violations. In practice, the state police are usually responsible for enforcing access regulations, although most states reported that local police have the authority to do so if they choose. Of the 35 states and the District of Columbia that regulate access, 19 reported having special commercial enforcement units within state police departments that are responsible for enforcing truck size and weight limits, and six states reported that local police actively enforce state access regulations. In most states fines for access violations are between $100 and $200. Summary Ten states have formally defined "terminal" (in legislation or in regula- tions) in a way that limits the use of STAA vehicles off the National Network and state-designated highways. In practice, however, most of
54 PROvIDING ACCESS FOR LARGE TRUCKS these states emphasize the adequacy of the roadway to accommodate STAA vehicles rather than the characteristics of the terminal itself. The procedures used by most states to provide access fall into two broad categories: (a) distance-based policies that allow STAA vehicles to travel within a specified number of miles from the National Network or other state-designated through-travel highways for access to terminals and service facilities (14 states) or (b) route-designation procedures whereby carriers normally apply for terminal access over specified routes, often supplemented by short (1- to 3-mi) distance limits for access to services (19 states and the District of Columbia). Although the distance- based approach has the advantage of being easy to implement and under- stand, simplifying enforcement and compliance and requiring no admin- istrative costs, the route-designation approach allows states to evaluate the adequacy of individual roads to accommodate STAA vehicles. To inform truck operators about which roads are open to STAA vehi- cles, several states publish maps or lists. Maps are commonly used to show the National Network and state-designated through-travel highways, whereas permitted access routes, because they tend to be short and may be open only to the permit holder, are typically identified in published lists. Although some states post signs to identify through-travel roads, they are rarely used to mark access routes because of the impracticality of signing many short road segments. Efforts to enforce access regulations vary greatly among jurisdictions. Enforcement is of most concern in the East where access regulations are most restrictive. In particular, many states have found it difficult to enforce regulations pertaining to STAA tractor-semitrailers, which, un- like twins, are difficult to distinguish from other large trucks. LOCAL ACCESS PROVISIONS As the data in Table 3-10 indicate, local governments (counties, cities, and towns) have jurisdiction over about 70 percent of the nation's road mileage, including about one-half of the Federal-Aid secondary system and three-fourths of the Federal-Aid urban system. Virtually all local streets are locally administered, but none is eligible for federal aid. Local governments in 18 states have authority, at least in principle, to independently regulate access on the roads under their jurisdiction (Table 3-11). Therefore, as a follow-up to the state surveys, telephone interviews were conducted with local highway officials representing county, city, and metropolitan planning organizations in 12 of these states.
TABLE 3-10 ROAD MILEAGE CLASSIFIED BY FEDERAL-AID SYSTEM AND JURISDICTION, 1987 (Highway Statisitics 1987 1988, 113-115, 134-136) Federal-Aid System Other Non-Federal-Aid Jurisdiction Interstate Primary Secondary Urban Roads Total State 44,328 254,961 196,226 34,061 269,588 799,164 Local 0 2,690 201,449 113,849 2,544,203 2,862,191 Federal 0 469 654 69 211,479 212,671 Total 44,328 258,120 398,329 147,979 3,025,270 3,874,026
56 PROVIDING ACCESS FOR LARGE TRUCKS TABLE 3-11 STATES CLASSIFIED BY LOCAL GOVERNMENT AUTHORITY TO DEFINE ACCESS Local Government Region Authority No. West Midwest East Hawaii Indiana Idaho Louisiana Montana Missouri Nevada Nebraska New Mexico North Dakota Utah Oklahoma Wisconsin State grants access 10 Alaska Arkansas with local input South Dakota Arizona Illinois California Iowa Colorado Kansas Oregon Michigan Washington Minnesota Wyoming Ohio Texas Connecticut Delaware Georgia Maryland Massachusetts Mississippi New Jersey North Caroliiia Vermont Florida Kentucky Maine New York Rhode Island South Carolina Virginia Alabama New Hampshire Pennsylvania Tennessee West Virginia State grants access 22 with no local involvement Local 18 governments have authority to define access on routes under their jurisdiction Extent of Local Involvement Responses to the interviews and surveys indicate that few local govern- ments have developed access policies for STAA vehicles. Local regula- tions, where they do exist, vary widely and often reflect special local conditions. Among the kinds of local restrictions reported were Local truck routes: Several local governments reported that large trucks are restricted to specified highways for through travel, although in most cases these restrictions apply to all large trucks not just to STAA vehicles. Most of these restrictions do not prohibit STAA vehicles from using local roads and streets for access to terminals and service facilities.
Policies and Practices 57 Truck bans: Local governments reporting broad prohibitions on STAA vehicles or large trucks in general included Boston, which limits twins' activity during peak travel periods (rush hours); New York City, where twins are prohibited from all city streets and roads unless specially permitted; and Los Angeles, which is considering a peak-hour limitation on all truck travel, including that of twins and STAA tractor-semitrailers, on city streets. Access approval: In some cities truck operators must apply for permission to use STAA trucks on local roads. For example, Philadelphia limits 102-in. -wide vehicles to roads reviewed and approved by city offi- cials in response to requests of carriers and shippers; Portsmouth, New Hampshire, restricts the use of twins to specially permitted routes; and Salinas, California, signs local access routes that have been evaluated and approved for longer STAA tractor-semitrailers on the basis of test runs of these vehicles over local roads. For the most part, local regulations are not directed at STAA vehicles specifically but are part of a general policy for controlling the use of all large trucks on local roads. Where special regulations for STAA vehicles have been adopted, they often reflect concerns brought to the attention of local governments on a case-by-case basis rather than a comprehensive truck access policy. Several local officials reported that truck access regulations, where they do exist, are ineffective when local police do not have adequate resources or knowledge of trucks to enforce them. Some also reported that the cost of signing access roads or providing permits for access can be prohibitive for local governments. Finally, because local economies may be adversely affected by truck limits, local officials are often willing to work with carriers and shippers to negotiate acceptable access policies. Thus, as STAA vehicles have be- come familiar, many access arrangements have been worked out for locations that were initially blocked by local regulations. Industry Concerns over Local Involvement Most state trucking associations reported that local access regulations are seldom as troublesome as state regulations, but many, nevertheless, expressed concern over the delays and administrative costs that are fre- quently the result of local regulations. Trucking associations in several states reported that local governments have adopted their own methods
58 PROVIDING ACCESS FOR LARGE TRUCKS of identifying access routes and application procedures for access, which make compliance with local regulations both time consuming and admin- istratively burdensome. In addition, many complained that local govern- ments take more time to review access requests than do states and seldom specify the criteria used to conduct reviews, which causes carriers to question the ability of some local governments to make fair and techni- cally sound judgments about access. State and Local Interaction Many of the local officials interviewed were not familiar with the operat- ing characteristics of STAA vehicles and therefore expressed a need for more state assistance in the form of guidelines and criteria for evaluating the adequacy of local roads to accommodate these vehicles. Responses to the state surveys suggest that only a few states are provid- ing local governments with such assistance. Among the more active states in this regard is California, which offers local governments both informa- tion about the operational characteristics of STAA vehicles and technical tools for evaluating proposed routes, and will assist with the evaluation of local access routes if local governments do not have the capacity to do so themselves. Other active states include Oregon, which, on request, will act as liaison between local governments and carriers and provide a centralized, "one-stop" procedure for access application, and Pennsylva- nia, which requires local governments to respond to access requests within 30 days or the requests are automatically approved. Summary Eighteen states reported that local governments have independent au- thority to define access policies on roads over which they have jurisdic- tion; however, few local governments actually exercise this authority. Judging from interviews with representatives of local governments and state trucking associations, more state assistance in developing local access policies would be welcomed. In many cases local governments lack the technical expertise to conduct route reviews and provide carriers with timely and consistent responses to access requests. To fill these gaps, some states are providing a central point to which carriers may apply for both state and local access, placing specific time limits on local access
Policies and Practices 59 reviews, and offering technical guidance and assistance in evaluating local access roads. SUMMARY OF FINDINGS State and local governments have responded to federal requirements that reasonable access be provided to STAA vehicles off the National Network by implementing a wide range of access policies. Major findings on the extent of highways open to STAA vehicles, the primary methods used by states to define and implement access provisions, and the key elements of access policies in those states that appear to have balanced the concerns and needs of both government and industry are summarized in this section. Extent of Roads Open to STAA Vehicles All roads open to STAA vehicles can be grouped under the following three categories: (a) the National Network, which includes virtually all Interstate highways and portions of the non-Interstate FAP system desig- nated by the U.S. Secretary of Transportation; (b) highways indepen- dently designated by the states for through travel by all, or some, STAA vehicles; and (c) specific access routes that connect through-travel high- ways with terminals and service facilities. Because a large portion of the FAP system has been placed on the National Network and state-designated through-travel systems, STAA vehicles can travel extensively on most of the country's major highways. Nationwide, more than 70 percent of FAP mileage is open to these vehicles. However, there are sharp regional differences. Western and midwestern states have opened more than 90 percent of their primary highways to all STAA vehicles. Eastern states allow twin trailer trucks on approximately one-third, and STAA tractor-semitrailers on approx- imately one-half, of their primary highways. Regional differences in the amount of highways open to STAA vehicles reflect such factors as prior experience with certain vehicles, particularly twin trailer trucks, and variations in highway and traffic conditions that affect the perceived adequacy of highways to accommodate the larger STAA vehicles. Disputes over the extent of access provided to these vehicles have been most heated in eastern states that limit through travel and provide short distances for access to terminals and services.
60 PRovIDING ACCESS FOR LARGE TRUCKS State Access Provisions Fifteen states allow STAA vehicles to travel virtually unrestricted on all public roads. The remaining 35 states and the District of Columbia have adopted a wide range of access policies. Important differences among states exist in the following areas: Definition of "terminal": About one-third of the states defines "ter- minal" in legislation or in regulations. In about half of these states the term is broadly defined as a "point of loading and unloading," and the remaining states define terminal in more precise terms, usually as a means of limiting the use of STAA vehicles on city streets and other high- traffic areas. In practice, however, most states emphasize the ability of the road to accommodate the vehicle rather than the characteristics of the terminal. Procedures for providing access: Procedures used by most states to provide access can be grouped into two broad categories: (a) distance- based policies that allow STAA vehicles to travel within a specified number of miles from the National Network or other state-designated highways to access terminals and service facilities and (b) route-designa- tion procedures, whereby the adequacy of individual roads to accommo- date STAA vehicles is evaluated by highway officials, frequently in re- sponse to requests of carriers or shippers. Distance-based policies have been adopted by 14 states, mostly in the Midwest and the West, as their primary method of providing access from the National Network or other state-designated through-travel highways. These policies have the advan- tage of being easy to implement and understand, but they are often considered arbitrary and may not prevent vehicles from operating on substandard roads. Route-designation policies, which allow access on approved routes only, are the primary way 19 states and the District of Columbia provide access to terminals and other destination points. Seven of these states have reviewed the adequacy of large portions of their highway systems for STAA vehicle travel; the other 12 states, all in the East, and the District of Columbia approve access on a route-by-route basis on request. Route-designation policies allow states greater control over the routes open to STAA vehicles than do distance-based policies, but they require substantially more technical and administrative support to implement and can be burdensome and confusing to carriers. Implementation: Efforts to communicate and enforce access provi- sions vary from state to state. Maps are commonly used to show the National Network and state-designated through-travel highways; permit- ted access routes, because they tend to be short and may be open only to
Policies and Practices 61 the permit holder, are usually identified in published lists. Although a few states use signs to mark terminal access roads, most do not because of the cost and impracticality of signing a large number of short road segments. Enforcement of access regulations is a concern in many eastern states where such regulations are most restrictive. Local Access Provisions Although local governments in 18 states have authority to regulate access, few exercise this authority, and local access policies are therefore not an issue in most states at this time. Nevertheless, where local regulations do exist, they may cause troublesome delays and administrative burdens for some carriers. Truckers claim that many local governments lack the technical expertise to conduct route reviews and provide timely responses to access requests. Survey responses suggest that a more active state role in coordinating local access arrangements might be welcomed by both local governments and the trucking industry. Examples of efforts by states to improve local access provisions include a centralized, or "one-stop," procedure for handling applications for state and local access (Oregon), specific time limits on local route reviews (Pennsylvania), and technical assistance in evaluating local access roads (California). Key Elements of Access Policies The analysis of state and local access policies and trucking industry responses suggests that access policies work best when they have the following characteristics: A through-travel network composed of the major highways connect- ing urban centers. Because major highways account for a large share of all large-truck traffic, some states have placed most FAP highways on the- National Network or on state-designated truck networks to accommodate the through-travel needs of carriers. Access has been least controversial in states where the majority of FAP highways are open to STAA vehicles. Explicit policies for providing access that are applied in a consistent and timely manner. Access policies are generally not perceived as arbi- trary if evaluation criteria are made explicit and are consistently applied. Because the time and administrative cost of applying for access can affect the restrictiveness of access regulations as much as the written policies,
62 PROVIDING ACCESS FOR LARGE TRUCKS practical restrictions are less severe in states in which access is provided in a timely manner and where state officials play a strong role in coordinat- ing local access arrangements. Access policies that can be simply communicated and enforced. Access disputes between industry and government officials are often the result of confusion over the roads open to STAA vehicles. In states where access policies are simple and easy to understand, and where access roads can be clearly identified, carriers reported the fewest problems complying with access regulations and, similarly, state highway and law enforcement officials reported the fewest problems implementing and enforcing access regulations. Mechanisms for industry and government to resolve access prob- lems. Many of the disputes between states or local governments and carriers are being resolved through negotiation and increased familiarity with, and acceptance of, STAA vehicles. Trucking associations in states that have established formal mechanisms for industry and government to negotiate differences report noticeable improvements in access arrange- ments. NOTES Highways can also be classified by their function in serving the flow of traffic through a road network. Functional classifications, as defined by the FHWA, are arterial highways, which generally serve longer trips; collector roads, which gather and disperse traffic between arterial highways and lower-order roads; and local roads and streets, which serve residential and other local areas (Highway Statistics 1987 1988, 114). The Tandem Truck Safety Act of 1984 provided a mechanism by which states could exempt from the National Network segments of the Interstate system that were deemed incapable of safely accommodating STAA vehicles. However, except for minor exceptions, all Interstate highways are on the National Network. When enacting legislation to comply with the 1982 STAA, 16 statesâArkansas, Colorado, Hawaii, Indiana, Kansas, Louisiana, Mississippi, Montana, Nebraska, Nevada, Ohio, Oklahoma, South Dakota, Texas, Washington, and Wyomingâ chose to uniformly adopt the federal limits (or greater ones) on all FAP highways and, in some cases, on all public roads. In addition, Iowa and New Mexico have placed more than two-thirds of their primary mileage on the National Network (89 and 69 percent, respectively). Nine statesâArizona, California, Idaho, Illinois, Michigan, Minnesota, North Dakota, Oregon, and Utahâhave imposed few practical limits on STAA vehicles. Where limits do apply, they primarily affect a relatively small number of twins exceeding 75 ft in overall length and tractor-semitrailers with long wheelbases or overall lengths exceeding 65 ft. Before the 1982 STAA, twin trailer trucks were prohibited on virtually all high- ways in 14 statesâConnecticut, Florida, Georgia, Maine, Massachusetts, New
Policies and Practices 63 Hampshire, New Jersey, North Carolina, Pennsylvania, Rhode Island, South Carolina, Vermont, Virginia, and West Virginiaâand the District of Columbia. Although New Jersey did not specifically ban twins, its 55-ft truck length limit effectively barred the industry-standard 65-ft twin. Massachusetts and New York allowed twin trailer trucks on state turnpikes, but the trailers had to be decoupled and pulled separately when they left these highways. Several states, other than these 14, restricted twins to designated networks. Fifteen states effectively banned 48-ft semitrailers: Alaska, Connecticut, Florida, Georgia, Maine, Maryland, Mas- sachusetts, Minnesota, New Hampshire, New Jersey, New York, North Carolina, South Carolina, Virginia, and West Virginia. Only 10 statesâConnecticut, Ha- waii, Idaho, Maine, Montana, North Dakota, Oklahoma, Rhode Island, Ver- mont, and Wyomingâallowed the operation of 102-in-wide trucks (TRB 1986, 26-28). See Chapters 6 and 9 and Appendix E for a more detailed discussion of the problems of vehicle offtracking and maneuverability and the effectiveness of regulating wheelbase dimensions. In many eastern states, regulations affecting STAA tractor-semitrailers are much less restrictive than those imposed on twins. In comparison, only a handful of states (California, Idaho, and New Mexico) has placed more restrictive limits on tractor- semitrailers than on twins; these limits, however, are not nearly as stringent as the limits imposed on twins by eastern states. The travel lanes of practically all Interstate highways are 12 ft or more wide. Comparable data on traffic volumes are not available for other Federal-Aid systems (secondary and urban). Arkansas, Colorado, Hawaii, Indiana, Kansas, Mississippi, Montana, Nebraska, Nevada, Ohio, Oklahoma, South Dakota, Texas, Washington, and Wyoming. See Chapter 4 for a detailed discussion of the use of twins and less-than-truckload terminal operations. California signs both tenninal and service access routes, estimated at an installed cost of $100 per sign (personal communication with Chief, Truck Operations Branch, California Department of Transportation, January 26, 1989). REFERENCES ABBREVIATIONS FHWA Federal Highway Administration TRB Transportation Research Board U.S. DOT U.S. Department of Transportation Federal Register. 1988. Vol. 53, No. 71, April 13, pp. 12,145-12,149. Highway Statistics 1987. 1988. FHWA, U.S. Department of Transportation. TRB. 1986. Twin Trailer Trucks. Special Report 211. National Research Council, Washington D.C., 388 pp. U.S. DOT (FHWA). 1984. Truck Size and Weight, Route DesignationsâLength, Width and Weight Limitations. Code of Federal Regulations, Title 23, Chapter 1, Part 658, June 5.
STAA Vehicle Use and Productivity T HE TWIN TRAILER TRUCKS and larger tractor-semitrailers authorized by the 1982 STAA provide an opportunity for major productivity improvements in certain segments of the trucking industry and for subsequent reductions in freight transportation costs to some shippers. Carriers and shippers claim, however, that the restrictive- ness of some truck access policies has created arbitrary limits on the use of STAA equipment that are insensitive to industry needs and have resulted in higher trucking costs. To address these issues, the discussion in this chapter Provides an overview of the characteristics and structure of the trucking industry; Examines the use of STAA vehicles by, and the benefits to, various segments of the trucking industry and shippers; Evaluates the impact of access regulation on carrier and shipper operations to identify the parties most adversely affected by access limits, to provide examples of the types and severity of problems created, and to estimate the impact on freight transportation costs; and Suggests ways that access policies could be better tailored to carrier and shipper operations and thereby reduce unnecessary costs. Much of the information in this chapter was drawn from in-depth tele- phone interviews of selected carriers and shippers likely to benefit most from the use of STAA equipment and thus likely to be the most adversely affected by access regulation. 65
66 PROVIDING ACCESS FOR LARGE TRUCKS CHARACTERISTICS AND STRUCTURE OF THE TRUCKING INDUSTRY Trucking is a major and versatile component of the freight transportation system. During the past few decades the share of freight carried by truck has grown steadily as the highway system has been developed, automotive technologies have been improved, and shippers' needs have changed. Trucking now accounts for about one-third of the ton-miles of all intercity freight traffic (Figure 4-1) and nearly three-quarters of all intercity freight transportation costs (Transportation Policy Associates 1988, 4). As the trucking industry has grown, the physical characteristics of trucks have changed. Tractor-semitrailers replaced straight trucks (a truck with the cab and cargo unit on a single chassis) as the predominant intercity freight vehicle in the 1930s (TRB 1986, 35); in the decades that followed, twin trailer trucks and other multitrailer vehicles were intro- duced on the highways (Figure 4-2). Today, businesses of all kinds depend on combination trucks to carry intercity freight and for some local car- riage. In 1987 approximately 1.4 million combination trucks (counted by the number of power units) were registered in the United States; major 100 90 in 80 z 0 70 U. 60 I- z w 50 cc CL 40 LU 30 20 0 10 Water Rail 29 35 40 45 50 55 60 65 70 75 80 84 YEAR FIGURE 4-1 Growth of the trucking industry's share of domestic intercity freight, 1929 to 1987 (TRB 1986; Roberts and Fauth 1988, 331); freight moved by air and pipeline has been excluded.
STAA Vehicle Use and Productivity 67 *k* Straight truck OW UJOW Straight truck withfull trailer *54* Three-ale tractor-semitrailer Five-axle tractor-semitrailer PRVOU Twin trailer truck FIGURE 4-2 Truck types (TRB 1986, 213). users were involved in for-hire transportation, manufacturing, construc- tion, agriculture, and wholesale and retail trade (Table 4-1). Trucking has evolved into a diverse industry composed of many differ- ent sectors that have correspondingly different operating characteristics and equipment requirements. Thus, before analyzing how STAA vehicles are being used, it is necessary to look more closely at the trucking industry itself and how its constituent segments operate.
68 PROVIDING ACCESS FOR LARGE TRUCKS TABLE 4-1 COMBINATION TRUCKS AND MILES BY MAJOR USE, 1987 (Census Bureau 1984; Highway Statistics 1987 1988, 171) Use No. Share (%) Miles (millions) Share (%) Agriculture 106,388 7.5 4,835 5.6 Forestry and lumbering 39,718 2.8 2,072 2.4 Mining 31,208 2:2 1,122 1.3 Construction 119,155 8.4 3,626 4.2 Manufacturing 139,015 9.8 9,497 11.0 Wholesale 148,944 10.5 8,460 9.8 Retail 52,371 3.7 3,799 4.4 For hire 683,724 48.2 49,815 57.7 Other (utilities, rental, services, not reported) 97,877 6.9 3,108 3.6 Total 1,418,514 100.0 86,334 100.0 Nom: Trucks counted by number of tractors and heavy single-unit trucks used regu- larly in combination with trailers. The total numbers of trucks and truck-miles are based on FHWA data for 1987; the percentage shares by major use are based on Census Bureau statistics compiled in 1982. Columns may not add to totals because of rounding. T'pes of Carriers The two major types of carriers are private carriers, companies whose primary business is not trucking but who operate their own fleets to move goods they produce or sell, and for-hire carriers, companies whose princi- pal business is transporting goods for others. Since deregulation of the trucking industry, each of these segments has undergone significant change and the distinctions between them have become blurred. Private Carriers Combination trucks are operated extensively by companies in a wide variety of businesses. Because of the control over service, equipment, and schedules that private fleets provide, many companies value their private carrier operations. Major operators include the nation's largest grocery and retail chains, manufacturers, oil companies, and wholesalers and distributors. Nearly one-half of the approximately 1.4 million combina- tion trucks registered nationwide is classified as private and accounts for the majority of all local carriage (trips of less than 50 mi) and about one- third of all intercity (trips of 50 mi or more) truck traffic (Table 4-2).
STAA Vehicle Use and Productivity 69 TABLE 4-2 COMBINATION TRUCKS AND MILES BY TYPE OF CARRIER AND RANGE OF OPERATION, 1987 (Census Bureau 1984; Highway Statistics 1987 1988, 171) Type of Carrier and Range of Opera- tion No. Share (%) Miles (Mi!- lions) Share (%) Private Local 337,606 23.8 10,878 12.6 Intercity 299,307 21.1 22,533 26.1 Subtotal 636,913 44.9 33,411 38.7 For hire Local 194,336 13.7 6,216 7.2 Intercity 489,388 34.5 43,599 50.5 Subtotal 683,724 48.2 49,815 57.7 Other 97,877 6.9 3,108 3.6 Total 1,418,514 100.0 86,334 100.0 NOTE: Trucks counted by number of tractors and heavy single-unit trucks used regu- larly in combination with trailers. The total numbers of trucks and truck-miles are based on FHWA data for 1987. Percentage shares by carrier type and range of operation are based on Census Bureau statistics compiled in 1982. Altogether, private carriers account for about 40 percent of the mileage traveled by combination trucks annually. For-Hire Carriers Although private and for-hire carriers operate roughly the same number of combination trucks, the for-hire segment is the largest segment of the trucking industry in terms of miles traveled. Approximately 60 percent of all miles traveled by combination trucks is by for-hire carriers, who are responsible for the majority of all long-distance, intercity truck traffic (Table 4-2). Traditionally, for-hire companies have specialized in either common or contract trucking. Common carriers transport goods for the public and charge published rates (tariffs); contract carriers haul goods for specific companies under contract. To operate in interstate commerce, both common and contract carriers must have Interstate Commerce Commis- sion (ICC) permission and are subject to regulations on markets they can serve, commodities they can carry, and prices they can charge. Independent contractors, or owner-operators, are a small but impor- tant share of the for-hire industry. Estimates suggest that there may be as
70 PROVIDING ACCESS FOR LARGE TRUCKS many as 100,000 Owner-Operators, who account for 10 to 15 percent of for- hire truck travel (TRB 1987, 16; Census Bureau 1984,40, 96). According to estimates provided by the Owner-Operator Independent Drivers As- sociation, most owner-operators regularly lease their services to larger carriers or haul certain goods, particularly agricultural commodities, that are exempt from ICC regulation (TRB 1987, 16). Trucking Services Most for-hire and private carriers specialize in one of two general kinds of shipments: truckload (TL) freight, a single shipment of which Constitutes the entire load of one truck,' and less-than-truckload (LTL) freight, which is composed of small shipments several of which make up the full load of a truck.2 Truckload Carriers Carriers of TL freight account for between 85 and 90 percent of all combination truck miles traveled, including virtually all private truck travel and the majority of for-hire travel (Table 4-3). Cargo carried in TL shipments includes a wide variety of commodities ranging from building materials and machinery to farm products and processed foods. More than 90 percent of all freight moved by combination trucks originates in truckload lots (Figure 4-3). Carriers that specialize in TL freight normally pick up a load in a line- haul truck (combination truck) at the shipper's dock and move it directly TABLE 4-3 COMBINATION TRUCK TRAVEL BY TYPE OF CARRIER AND TRUCKING OPERATION (Census Bureau 1984; Highway Statistics 1987 1988, 171) Private For-Hire Total Miles Share Miles Share Miles Share Operation (millions) (%) (millions) (%) (millions) (%) TL 33,400 100 39,800 80 73,200 88 LTL 0 0 10,000 20 10,000 12 Total 33,400 100 49,800 100 83,200 100 Nare: Estimates do not include approximately 3,100 million miles reported as "other" (see Table 4-1).
30 25 STAA Vehicle Use and Productivity 71 0I I I I I I I 1980 1981 1982 1983 1984 1985 1986 1987 YEAR FIGURE 4-3 Freight movement by type of operation (Roberts and Fauth 1988, 342). to the receiver or receivers in the same vehicle; they seldom handle freight at their own facilities, which are typically few in number and far removed from origins and destinations of shipments (Office of Technology Assess- ment 1988, 49). Because of the nature of TL operations, many TL carriers lack substantial investment in communications, management, and sales forces, and depend on the services of owner-operators for equipment and drivers (Office of Technology Assessment 1988, 48). These drivers may not be thoroughly trained in the particular handling and performance characteristics of the new STAA equipment. The large, fragmented TL sector is composed of many small and medium-sized carriers. Estimates suggest that there are more than 25,000 for-hire carriers and 50,000 private carriers providing TL services (Office of Technology Assessment 1988, 34),3 ranging from specialized opera- tions, such as petroleum and automobile carriers, to more familiar and versatile van and flatbed carriers that haul a wider variety of commodities and account for most truckload mileage (Table 4-4).
72 PROVIDING ACCESS FOR LARGE TRUCKS TABLE 4-4 SHARE OF TL COMBINATION TRUCK MILEAGE BY TRAILER BODY TYPE (Census Bureau 1984) Share of Truck Miles Trailer Body Type (%) Van (enclosed, open, and refrigerated) 52 Flatbed and platform 26 Tank and hopper 17 Other 5 Less-than- Truckload Carriers The specialty of LTL carriers is transporting smal1-hipment freight in units that generally weigh anywhere from 250 to 12,000 lb (Office of Technology Assessment 1988, 47)4 These shipments are usually com- posed of general freight cargoes from several shippers that are bound for many different destinations. To minimize line-haul miles and the number of handlings of freight, LTL carriers maintain extensive networks of strategically located termi- nals and operate combination trucks on regularly scheduled line-haul routes between terminals. Shipments are initially carried by smaller pickup and delivery trucks to local outbound terminals where they are sorted and consolidated into truckload-sized lots and loaded onto combi- nation trucks for line haul. At intermediate terminals (breakbulk or consolidation centers) these loads are reconsolidated and directed to inbound terminals, where they are broken down for local delivery. Be- cause shippers of LTL freight are often service sensitive (for example, shippers may request special handling or 1-or 2-day service), LTL carriers pay special attention to maintaining reliable equipment (for example, they have preventive maintenance programs and own equipment instead of relying on owner-operators); hiring, training, and retaining high-qual- ity personnel; and establishing sophisticated communications and dis- patching operations (Office of Technology Assessment 1988, 48). The large investment in terminal operations required of LTL carriers makes entry into the business difficult. As a result, some of the companies in the LTL sector are quite large (United Parcel Service, Yellow Freight, Roadway Express, and Consolidated Freightways). In sharp contrast to the fragmented TL business, the entire LTL industry is composed of fewer than 500 companies (Desmond 1988, 98), of which about 100 are national or transcontinental carriers and the remainder are smaller re-
STAA Vehicle Use and Productivity 73 gional carriers that provide high service levels or serve special market niches (Hoffman 1988, 12-14). Impact of Deregulation Recent legislative and administrative changes in federal trucking regula- tion have had a profound impact on all aspects of the trucking industry. The most significant legislative action was passage of the Motor Carrier Act of 1980, which greatly relaxed ICC constraints. Important changes stemming from this legislation were simplified entry into the industry, greater pricing freedom, expanded classification of exempt commodities, provision of for-hire services by private fleets, and easing of territorial restrictions. Since deregulation, the trucking industry has undergone substantial reorganization. Established carriers have been given more flexibility to provide new services, and many private carriers and owner-operators can now operate independently as for-hire interstate carriers. As a result, the number of ICC-authorized carriers has more than doubled during the past decade, from about 17,000 certified carriers in 1979 to 38,000 in 1987 (Table 4-5). Although the competitive pressures encouraged by open market entry helped keep trucking prices down, they forced many for-hire carriers to operate below cost and subsequently fail. Other changes caused by dereg- ulation should have lasting effects: Recognizing the need to hold down costs, but still attract service-sensitive shippers, trucking companies are now paying more attention to marketing and providing more reliable and TABLE 4-5 NUMBER OF ICC-REGULATED MOTOR CARRIERS BY CLASS (Standley and Roman-Slavin 1988, 98; TRB 1986, 71) Year Class I II III Total 1987 856 1,266 35,505 38,338 1985 1,013 1,489 30,337 33,283 1983 1,139 1,631 24,411 27,517 1981 1,031 2,293 18,563 22,270 1979 992 2,754 13,337 17,083 NOTE: Class! carriers have annual revenues of more than $5 million; Class II, $1 million to $5 million; Class Ill, less than $1 million.
74 PROVIDING ACCESS FOR LARGE TRUCKS flexible services to shippers (Lane 1988, 11-14). Strong growth has been experienced by carriers engaged in contract trucking, many of whom tailor their services and equipment to the needs of major shippers (Roberts and Fauth 1988, 341-343; Murphy 1988, 10). Summary Trucking is a diverse business that serves many different transportation needs of a wide variety of industries. Traditionally, trucking companies have been classified as either for-hire or private; however, recent changes in economic regulation have eroded the relevance of many traditional distinctions, and carriers are now more appropriately defined by the market segments they serve. Today, trucking companies specialize in serving two virtually indepen- dent markets: truckload shippers and less-than-truckload shippers. A TL carrier normally picks up a truckload-sized shipment at the shipper's dock and delivers it directly to the receiver or receivers in the same truck. Smaller for-hire companies and private carriers that lack substantial investment in or need for terminal operations have historically provided TL service, which accounts for between 85 and 90 percent of all combina- tion truck miles traveled. Conversely, large for-hire trucking companies tend to specialize in hauling LTL freight. Because LTL freight consists of small shipments, several of which makeup the full load of one truck, LTL carriers must have networks of pickup and delivery fleets and terminals where cargo can be consolidated for line haul. Measured by miles of operation and volume of freight, the LTL sector is considerably smaller than the TL sector, and it accounts for less than 15 percent of combination truck miles traveled. Deregulation and the intense competition that has followed have forced both TL and LTL carriers to rethink the way they do business. Many carriers are now providing less costly and more efficient trucking services to remain competitive. The ways carriers have accomplished this include applying new business strategies that integrate marketing and operations and tailoring their services and equipment to the needs of major shippers. USES AND BENEFITS OF STAA VEHICLES Increased use of the larger trucks permitted by the STAA of 1982 has coincided with deregulation-induced changes in the trucking industry. Strong economic incentives have been an important determinant in the
STAA Vehicle Use and Productivity 75 trucking industry's conversion to STAA trucks since 1982. In the follow- ing subsections, a variety of sources, including trailer sales data and a series of motor carrier and shipper interviews conducted for this study (see Appendix D), is used to determine the extent of this conversion and the economic benefits it has provided. Conversion to STAA Vehicles Available sources suggest that a majority of carriers have made substan- tial investments in the new trailers permitted by the STAA. Trailer Sales Data Data on dry van sales, which account for about one-half of total trailer sales, indicate that the 48-ft semitrailer has become the most popular choice of carriers purchasing new van trailers. Sales data collected and published by the Truck Trailer Manufacturers Association (Truck Trailer Manufacturers Association 1988/1986) reveal that sales of 48-ft trailers, which were practically negligible in 1982, increased to 63 percent of total sales by 1988 (Table 4-6). During the same time, sales of 53-ft trailers increased from zero to 5 percent of the total, and the previous standard 45-ft trailer dropped from 75 to less than 10 percent of total sales. The data also indicate that twin trailers (28-ft units) now make up a significant portion of van trailer sales. Sales increased from about 8 percent of total sales in 1982 to 17 percent by 1988. Finally, more than 70 percent of all van trailer sales in 1988 were of 102-in.-wide trailersâan increase from nearly zero in 1982. Sales data on the dimensions of trailer body types other than vans are not available. TABLE 4-6 PERCENTAGE OF VAN TRAILER SALES BY TRAILER LENGTH (Truck Trailer Manufacturers Association 1988/1986) Year Length (ft) 1988 1986 1984 1982 53 5 2 1 0-1 48 63 52 56 1-2 45 9 13 16 75 28 17 26 22 8 Nom: Annual figures projected from survey data. Columns do not add to 100 because of other trailer lengths.
76 PROVIDING ACCESS FOR LARGE TRUCKS Carrier Interviews Because trailer sales statistics do not provide information about the uses of the new STAA equipment, 20 for-hire carriers were selected for in- depth interviews for this study. Included in this sample were 12 TL carriers and 8 LTL carriers that operate throughout the country. Al- though these trucking companies represent a small fraction of all carriers, they include many of the trucking industry's dominant and pace-setting companies, representing 8 of the top 50 TL carriers (measured by reve- nue) and 7 of the top 20 LTL carriers in the nation.6 As a group, they operate more than 150,000 trailers and move a wide variety of goods, ranging from food products to equipment and machinery. Truckload Carriers All 12 truckload carriers reported that the 48-ft semitrailer is becoming the truckload industry standard, especially for van trailer operations. Eight of these carriers reported operating van trailer fleets made up exclusively of 48-ft (or longer) semitrailers, and the remaining four had converted more than 75 percent of their van trailer fleets to these vehicles. All of the carriers that had not yet fully converted their fleets expected to do so within the next 5 years. Some carriers also reported increased use of the longer 53-ft trailers; however, none expected to convert exclusively to these trailers in the foreseeable future. Because of the operational disadvantages of using twins for hauling truckload shipments, which are discussed in following sections, most TL carriers had not purchased these vehicles and none planned to experiment with them in the future. Less-than-Truckload Carriers The carrier interviews indicate that the recent increase in use of twin trailer trucks has been confined mainly to LTL carriers. All eight LTL carriers reported using these vehicles on at least half of their line-haul trips, and four reported using them on more than 75 percent of their trips. Although some of the companies were using twins before 1982, most did not begin large-scale conversion until after passage of the STAA. Lower conversion rates were reported by smaller, regional carriers that had retained relatively large amounts of TL business or routes with low
STAA Vehicle Use and Productivity 77 volumes of freight traffic; however, even these carriers foresaw continued conversion to from 60 to 100 percent twins. On the other hand, the LTL carriers reported only minor purchases of the longer and wider STAA semitrailers. With the exception of two smaller companies that had purchased a modest number of 48-ft semi- trailers for use on low-volume traffic corridors, the LTL carriers expressed little interest in converting to STAA semitrailers, which lack both the operating flexibility and the carrying capacity of twins. Reasons for Conversion Because carriers select trailers largely on the basis of the characteristics of commodities they carry, the increased truck size limits permitted by the STAA have not been of equal interest to all carriers. To understand why some carriers are converting to the larger tractor- semitrailers and twin trailer trucks permitted by the STAA, it is important to look at commodity density. Because the larger STAA van trailers are considerably more spacious than the previous standard 45-ft by 96-in. trailer (a 48-ft by 102-in, van trailer provides 13 percent more cargo space, and a twin trailer truck offers about one-third more space), they are particularly attractive to carriers of low-density (lightweight and bulky) commodities who can carry considerably more cargo without "cubing- out" (filling all available cargo space before reaching the legal weight limit). A 45-ft trailer will normally cube out when carrying cargoes with a density of less than 17 lb/ft3; a twin trailer truck will not do so unless the cargo has a density of less than 12 lb/ft3 (Table 4-7). Examples of low-density cargoes that benefit from larger truck sizes are TABLE 4-7 CARRYING CAPACITY OF TYPICAL VAN TRAILERS Volume Cube-Out Trailer Dimensions Capacity Densityb [length (ft) by width (in.)] (ft3) (lbIft3) 45 x 96 3,100 17 48 x 102 3,500 15 53 x 102 3,900 13 Twin 28 x 102 4,200 12 Estimates are for enclosed van trailers with an interior height of 8.5 ft. density of cargo to fully load vehicle but not exceed gross vehicle weight limit (i.e., 80,000 Ib).
78 PROVIDING ACCESS FOR LARGE TRUCKS plastic and aluminum articles, empty containers, textiles, general freight (mixed cargoes), and household furniture and appliances. Shipments of low-density cargoes account for approximately one-third of all combina- tion truck miles traveled, including virtually all LTL carriage and about 20 percent of TL shipments (Table 4-8). STAA Semitrailers: TL Carriers As suggested by the carrier interviews, TL carriers have been rapidly converting to the longer and wider semitrailers permitted by the STAA. 48-ft Trailers Although the TL carriers interviewed reported carrying a wide range of commodities with varying densities, all indicated that 48-ft trailers have become vital to their operations. These trailers are particularly appealing TABLE 4-8 COMBINATION TRUCK MILES TRAVELED BY LOAD DENSITY AND TRUCKING OPERATION (Census Bureau 1984; Highway Statistics 1987 1988, 171) Load Density and Miles Trucking Operation (millions) Share (%) Low density TL 15,800 19 LTL 10,000 12 Subtotal 25,800 31 Medium to high density TL 57,400 69 LTL 0 0 Subtotal 57,400 69 Total 83,200 100 NOTE: On the basis of an analysis of truck weights and cargoes reported by the Census Bureau, it was assumed, for the purposes of this study, that all paper products, textiles, furniture, plastics, fabricated metals, machinery, transportation equipment, house- hold goods, and general freight (mixed cargoes) are low-density commodities, and that all farm products, animals, mining and forest products, foods, building materials, chemicals, petroleum, and primary metal products are medium- to high-density com- modities.
STAA Vehicle Use and Productivity 79 to carriers of low-density cargoes, because these trailers offer more cargo space than the previous standard 45-ft trailer, yet even carriers of predom- inantly heavy cargoes reported substantial conversion. For example, two midwestern carriers explained that by converting entirely to 48-ft trailers they maintain the flexibility to compete for both low- and high-density goods and avoid the logistic problems associated with tracking and bal- ancing mixed (45-ft and 48-ft) trailer fleets. The carriers noted that the productivity benefits associated with the more spacious 48-ft trailers are passed on to shippers. None reported charging shippers a premium for these vehicles. 53-ft Trailers Most of the carriers interviewed expect to make greater use of 53-ft trailers in the future. However, they varied greatly on whether these vehicles will make up a small or a large share of their fleets. Although they appeared to be reluctant to convert their entire fleets to 53-ft trailers so soon after making substantial investments in 48-ft trailers, most carriers indicated that their decisions to purchase 53-ft trailers will be largely influenced by the type of commodity they usually carry, state truck size regulations, and the extent to which shippers and receivers demand these vehicles and adjust their shipment sizes and loading facilities to handle them. Trucking company executives did not predict that the 53-ft trailer would become the truckload industry standard; they predicted that it would become the standard for TL carriers hauling primarily low-density cargoes. STAA Semitrailers: TL Shippers Nine shippers of low-density truckload freight were interviewed to pro- vide a picture of the benefits achieved by shippers using STAA semi- trailers. Included in this group were the largest shippers of lightweight containers and cans (accounting for about 20 percent of industry reve- nues), snack food products (accounting for more than one-third of indus- try revenues), breakfast cereals (accounting for approximately 40 percent of the industry), and bakery goods (accounting for 20 percent of the industry). All of the shippers reported that the additional cubic capacity of the longer and wider STAA semitrailers resulted in significant savings. Shippers of very light commodities, such as empty containers, clothing, and plastic products, derived the greatest benefits and reported reduc-
80 PROVIDING ACCESS FOR LARGE TRUCKS tions in line-haul costs directly proportional to the additional volume capacity provided by the STAA semitrailers. However, because not all shippers have sufficiently light cargoes or large enough shipment sizes to take full advantage of the more spacious STAA semitrailers, more modest reductions were reported by some companies. Overall, the shippers estimated that the shift from 45-ft trailers to the moderately more spa- cious 48-ft trailers had reduced line-haul trucking costs by 5 to 13 percent (about 8 percent average); shippers using 53-ft trailers estimated savings of about 20 percent, with possible savings of up to 26 percent under optimal conditions. Several shippers also reported that the additional width of STAA semitrailers facilitates loading and unloading cargo. The 102-in, trailers allow some commodities to be positioned in the trailer in a manner that not only increases payload capacity but also reduces cargo loading and unloading time. As an example, one company reported that because the pallets for its cargo are 48 in. long by 40 in. wide, when they are loaded onto 96-in, trailers (which typically have 92- to 94-in, interiors) they must be "pinwheeled," or stacked widthwise along one trailer sidewall and lengthwise along the other; the 102-in, equipment allows the pallets to be uniformly stacked sideways. The company estimated that this advantage reduces by one-third the time it takes to load and unload shipments. In addition, another shipper reported that the extra trailer width has permit- ted some pallet dimensions to be increased, allowing commodities to be stacked higher in warehouses and on trailers and thereby increasing warehouse and vehicle efficiency. Some company executives reported that the expanded use of larger semitrailers, particularly the 53-ft trailers, has added certain costs. For example, to operate 53-ft trailers between its manufacturing plants and warehouses, one company had to upgrade several older loading facilities and expand surrounding yard space. However, the majority of shippers maintained that these cost disadvantages are small compared with the total benefits they derive from using the larger trailers. Twin Trailers: LTL Carriers Before 1983, travel by twins averaged 3 to 4 percent of all combination truck miles traveled in the United States. The bulk of this travel occurred in California and some other western states where use of twins was largely unrestricted. Since passage of the STAA, travel by twins has grown substantially in many statesâmainly in the Eastâwhere these vehicles
STAA Vehicle Use and Productivity 81 had been largely prohibited, although these percentage increases still represent small traffic volumes. Nationwide vehicle counts indicate that twins accounted for between 5 and 6 percent of combination truck travel in 1986 (Table 4-9). Travel by twins remains unevenly distributed among geographic regions, reflecting the different uses of these vehicles in differ- ent parts of the country. In California the use of twins is almost as diverse as that of tractor- semitrailers; twins account for about one-third of the combination truck travel on rural Interstates (TRB 1986, 82). Until the early 1970s, twins had a considerable gross weight advantage over tractor-semitrailers be- cause of California's statutory axle weight and length limits. Also, twins are particularly well suited for use in some of California's specialized agricultural operations (TRB 1986, 74). California's experience with twins, however, appears to be atypical of that of other parts of the country where the use of twins has been confined mainly to LTL carriers. Data indicate that in the East more than 90 percent, and in the Midwest more than 75 percent, of the cargo carried in twins has been LTL freight (TRB 1986,74-87). Moreover, none of the TL carriers interviewed for this study knew of significant use of twins by TL carriers outside California and cited the following reasons: Because twin trailer trucks have high tare (empty) weights, they can quickly exceed gross vehicle weight limits when carrying high-density cargoes; Because the twin 28-ft trailers must be uncoupled and loaded and unloaded separately, they require additional loading stations and freight handlers; and TABLE 4-9 PERCENTAGE OF ALL COMBINATION TRUCK MILES TRAVELED BY TWIN TRAILER TRUCKS, 1986 (unpublished data, from FHWA) Highway System Other Region Interstate Arterial Other Total Western and Mountain 13.6 18.1 3.1 15.1 Central and Plains 4.4 3.6 1.6 3.8 Eastern 4.5 1.3 0.6 2.9 U.S. Total 6.1 6.1 1.4 5.7 NoTE: Figures may include some mileage by five- and six-axle double trailer trucks with trailers longer than 28 ft.
82 PROVIDING ACCESS FOR LARGE TRUCKS Because of the small size of single 28-ft trailers, they are used most efficiently in the twin trailer configuration and are too inflexible for most TL operations. In comparison, the LTL carriers interviewed reported that twin trailer trucks are particularly well suited for their operations. Twins provide two important benefits for these carriers: increased volume capacity and reduced freight-handling costs. Volume Capacity Because the average LTL shipment has a density of from 12 to 13 lb/ft3, a 45-ft by 96-in, semitrailer carrying LTL freight would cube out at about 10,000 lb below the gross vehicle weight limit of 80,000 lb (TRB 1986,71). With a set of twin trailers, which increases volume capacity by approx- imately one-third, an LTL carrier can haul considerably more freight without exceeding weight limits. Most of the LTL carriers interviewed, however, indicated that there is not always a one-to-one correspondence between added volume capacity and reductions in line-haul trips, because twins are not always operated fully loaded. Although none of the carriers could isolate the savings attributable to additional volume capacity, they noted that, because line- haul costs account for between one-third and one-half of total expenses, even slight reductions in line-haul trips can produce sizable savings. Terminal Efficiencies In addition to increased volume capacity, LTL carriers reported two other important advantages of twins over tractor-semitrailers:7 Shipments headed to two different terminals in the same general direction often do not need to be handled at intermediate freight recon- solidation (or breakbulk) centers. Freight can be delivered by the individual 28-ft trailers (pups) oper- ated separately instead of being unloaded from a longer semitrailer into a smaller delivery truck. These efficiencies have had an important influence on LTL carriers' decisions to convert to twin trailer trucks. All carriers reported using these vehicles to reduce freight handling at intermediate terminals, and
STAA Vehicle Use and Productivity 83 nearly all reported using single pups for a significant share of pickups and deliveries. Carriers estimated that the reduction in freight handlings resulting from use of twins ranged from 10 to 35 percent, reflecting different carriers' circumstances and uses of twins. Although few carriers could quantify the savings attributable to increased terminal efficiencies per se, they noted that, like line-haul costs, terminal and pickup and delivery costs are importantâthey account for between one-third and one-half of all expenses. A TRB report on twin trailer trucks estimated that the increased use of twins (assuming 75 percent of LTL trips are by twins) would decrease line- haul mileage by approximately 10 percent and freight-handling costs by about 6 percent (TRB 1986, 106-109). Although the benefits of twins would be decreased by the higher capital and operating costs of these vehiclesâfor example, twins have somewhat higher fuel and driver costs (drivers are normally paid an additional penny a mile for driving twins) and require more loading stations and yard space (to move and store pups) than do tractor-semitrailersâit was projected that the increased use of twins would result in a net reduction in LTL carrier costs of about 2 percent, or $500 million per year. The extent to which these cost reduc- tions would translate into savings for LTL shippers, however, has not been projected. Summary Carriers have begun a massive and rapid conversion of their fleets to the wider and longer trucks authorized by the STAA. Virtually all of the new van trailers sold since passage of the STAA in 1982 have been of the dimensions permitted by the act. The 48-ft semitrailer is rapidly replacing the 45-ft trailer as the TL industry standard. For-hire and private carriers who haul truckload ship- ments are using the more spacious 48-ft trailers to carry a wide variety of commodities. These trailers are particularly valued by shippers of light- weight commodities because they offer additional cargo space and resul- tant savings in transportation costs. Although 53-ft semitrailers are now legal in many states, their sales currently represent only a small portion of total trailer sales. However, carriers and shippers expect these longer vehicles to become increasingly popular for carrying truckload shipments of lightweight commodities, which account for about 20 percent of all truckload combination truck miles traveled. Shippers of lightweight com- modities estimated average reductions in line-haul costs on the order of 8 and 20 percent as a result of using 48- and 53-ft trailers, respectively.
84 PROVIDING ACCESS FOR LARGE TRUCKS Growth in the use of twins has been concentrated within the LTL segment of the trucking industry. Because of the nature of their opera- tions, LTL carriers can take advantage of the additional volume capacity of twins and the flexibility that dividing loads into smaller trailers allows to reduce line-haul mileage and terminal handling costs. Because line-haul and terminal costs can account for two-thirds or more of an LTL carrier's total costs, even slight reductions in these costs can produce sizable savings. The benefits of twins are valuable to LTL carriers who specialize in multiple small shipments of low-density freight. TL carriers, however, have found that the costs of integrating these vehicles into their opera- tions usually outweigh the benefits. For this reason, twins account for only about 5 to 6 percent of total combination truck travel. IMPACT OF TRUCK ACCESS POLICIES Despite the expanded use of STAA vehicles, it appears that some state and local access regulations are preventing some carriers and shippers from achieving the full productivity gains they expected as a result of passage of the STAA. Because of both the wide range of state access policies and practices and the variety of uses of STAA vehicles, it is not possible to precisely measure this impact; however, responses from car- riers and shippers provide an idea of the kinds of problems that result from access regulation and of the costs to carriers and shippers. Severity of Access Problems Judging from the interview responses, access regulations have not ad- versely affected the great majority of shipments by carriers using STAA equipment. As observed in Chapter 3, there appear to be several reasons for these responses: Mileage of through-travel highways open to twins and larger tractor- semitrailers is extensive in many states; Many states have lenient access policies that allow STAA vehicles on a wide range of roads; Efforts to enforce access regulations vary greatly among jurisdic- tions; some states are apparently suspending rigorous enforcement until the FHWA has completed its rulemaking on access; and
STAA Vehicle Use and Productivity 85 In many states initial disputes between state and local governments and truck operators are being resolved as STAA vehicles become more familiar and accepted. Nevertheless, access regulations, where they are restrictive, can affect the optimal use of STAA equipment. In particular, the following prob- lems were reported by carriers and shippers: Inability to access some terminals: New York and Pennsylvania were cited most often as states that deny STAA vehicles access to some truck- ing destinations. If trucking destinations cannot be legally accessed by STAA equipment, carriers are apparently discontinuing service to these locations; maintaining additional fleets of non-STAA equipment; or, in some cases, operating illegally. As an example, one LTL carrier reported operating two separate trailer fleets, one composed of twin trailers that are used throughout most regions of the country and another composed of semitrailers that service the company's northeastern terminals, where twins are prohibited. Circuitous routing and hours-of-service limitations: Several carriers cited instances in which state and local governments have designated lengthy access routes or confined access travel to off-peak hours, resulting in additional miles traveled and scheduling problems. One LTL carrier estimated that approximately one-quarter of its terminals must be ac- cessed by lengthy detoursâranging from 5 to 50 miâthat add more than 300,000 mi to the company's annual mileage figures; a TL carrier re- ported discontinuing service to some shippers in the Northeast because the extra miles added by access detours had made servicing these accounts unprofitable. Specific locations that are adversely affected by access restrictions include Oil City, Pennsylvania (25-mi detour); Thomasville, Georgia (46-mi detour); and Boston (no twins activity during peak periods). Time and administrative cost of applying for access: Carriers re- ported delayed responses to access requests and confusion resulting from the lack of uniformity in access regulations among states and localities. Carriers reported that applications may take 6 months or more to process in extreme instances, and that access is sometimes denied without expla- nation. The states cited most often as having notably slow or burdensome application procedures were Massachusetts, New York, and Pennsyl- vania.8 Uncertainty about access regulations and enforcement: Executives of several carriers expressed concern that access regulations and enforce-
86 PROvIDING ACCESS FOR LARGE TRUCKS ment in some states may become more stringent in the future. Although their companies have purchased STAA vehicles despite this uncertainty, they noted that this possibility has adversely affected decisions about purchasing equipment. One LTL carrier reported that until recently the company had been purchasing 96-in, twins instead of 102-in, units be- cause of access regulations in New York and Pennsylvania. Users Affected Access regulations have not had the same impact on all carriers and shippers. General findings from the interviews suggest there are notable differences among industry segments. TL Carriers and Shippers Estimates of the share of shipments adversely affected by access regula- tions varied among the TL carriers and shippers sampled. Seven of the 12 carriers and 5 of the 9 shippers reported no problems related to access regulation. Most of the nine companies experiencing difficulties esti- mated that between 5 and 20 percent of shipments are adversely affected by access regulation; one reported that as much as 30 percent was ad- versely affected. In particular, these companies reported problems in the following areas: Access application procedures: TL carriers emphasized that, unlike LTL carriers, they do not operate over regularly scheduled routes that make advanced permitting or route approvals practical. Especially af- fected are TL common carriers who frequently serve a wide variety of shippers and are seldom provided sufficient notice of shipping destina- tions to apply for access permission. In addition, many of the TL carriers reported having minimal communications and administrative staffs, which makes compliance with some state and local access procedures particularly burdensome. Distance-based access policies: For many TL carriers, access policies that limit travel to short distances from the National Network or state- designated through-travel networks can be problematic because of the location of many truckload origins and destinations. Most carriers esti- mated that only a small share of their customers can be reached within short mileage limits; seven reported that fewer than 20 percent are located within 2 mi of a designated through-travel highway.
STAA Vehicle Use and Productivity 87 Terminal definitions: Because some states define "terminal" so as to exclude many truckload destinations, TL carriers expressed concern that these definitions could become troublesome. TL carriers emphasized that, unlike LTL carriers, they do not maintain their own terminals for freight consolidation and breakbulk as defined in some state regulations; they normally depend on shipper and receiver facilities for direct loading and unloading. Although none of the carriers reported any serious diffi- culties stemming from existing definitions as now interpreted, they were concerned that these definitions might be more stringently applied in the future. Information: Inadequate information about access regulations was noted as a serious problem by all of the TL carriers interviewed. Several reported that existing mechanisms for identifying access routes are inap- propriate for TL operations. Specifically, carriers reported that extensive lists of approved access routes, published by some states, are impractical because they are often out-of-date and too lengthy for drivers and dis- patchers to use regularly. Although maps are useful for identifying through-travel highways, carriers noted that they do not show shorter terminal access routes and often become outdated quickly. As an alterna- tive, several carriers suggested that state and local governments use consistent signs to indicate access routes. LTL Carriers The eight LTL companies in the sample varied in their estimates of the impact of access regulations. Half reported no problems with access, noting that the size and extent of the National Network and the charac- teristics of the freight markets they serve are the primary factors that determine their use of twins. According to these carriers, access regula- tions have not created serious problems for the following reasons: These carriers normally operate over a network of regularly sched- uled routes and have worked out most access arrangements through negotiation with state and local officials who, over time, have become increasingly familiar with and accepting of twins; LTL terminals are strategically located near designated highways and therefore are seldom located beyond access distance limits; and Published lists are sufficient for route identification because LTL drivers regularly run the same line-haul routes. Nevertheless, where restrictive access regulations do exist, they can have a greater impact on LTL operations than may be obvious. Two
88 PROVIDING ACCESS FOR LARGE TRUCKS carriers estimated that as much as 30 percent of their shipments is ad- versely affected by access regulations that prevent them from dispatching twins to several key terminals. These carriers noted that because they structure their line-haul operations by terminal groupings, whereby vehi- cles are shuttled between several terminals to minimize travel time and vehicle miles, access limits at just one terminal can affect scheduling and equipment usage at several terminals. For instance, if a carrier uses twins between most of its terminals, but must use tractor-semitrailers to access a restricted terminal, the trailer fleet becomes unbalanced unless there is substantial movement of empty trailers between terminals. In such situa- tions, the carrier might opt to use tractor-semitrailers in order to maintain complementary equipment and avoid systemwide schedule disruptions. One carrier presented evidence indicating that restrictive access regula- tions affecting terminals in Pennsylvania resulted in additional terminal and line-haul costs of about $600,000 per year [Consolidated Freightways v. Larson, 647 F.Supp. 1479 (M.D. Pa. 1986) 1519, Exhibit CF-2011]. When asked how they thought regulations should be revised, most LTL carriers recommended that more highways be placed on the National Network or on state through-travel networks and that more consideration be given to the total impact of access regulations on truck travel and use. Also, because they have made substantial investments in twin trailer trucks, which receive considerable local government attention, many of the LTL carriers recommended that local route reviews be based on technically sound evaluation criteria that are consistently applied. Productivity Losses to Major Users of STAA Vehicles An important cost of truck access regulation is its deterrent effect on carriers' and shippers' decisions to use STAA vehicles. However, re- sponses during the interviews suggest that, because access problems are not widespread but are concentrated in relatively few states, only a small number of major users of STAA vehiclesâTL carriers of low-density freight and LTL carriersâare adversely affected by these regulations. Judging from these interviews, a reasonable estimate might be that these carriers are not using STAA vehicles on 5 percent of their trips because of, restrictive access policies.9 For TL carriers of low-density freight, the major users of 48-ft semi- trailers, 5 percent of all trips amounts to about 800 million miles per year [0.05 x 16 billion miles (see Table 4-8)], which presumably would be reduced by some fraction if truck access problems were resolved and the more spacious 48-ft semitrailers could be used on these trips.10 Under
STAA Vehicle Use and Productivity 89 optimal conditions, all 13 percent of the additional cargo space provided by 48-ft semitrailers (compared with the previous industry-standard 45-ft semitrailer) would be used, and this mileage would be reduced by about 100 million miles per year (0.13 x 800 million miles). Assuming trucking line-haul costs of about $1 per mile (Lane 1988, 12), the cost of access regulation to shippers and carriers of low-density freight would be on the order of $100 million per year. Estimating the cost of access regulation to the LTL industry, the major users of twin trailer trucks, is more complicated because of the combined benefits of line-haul and freight-handling savings. Nevertheless, a rough approximation can be made using TRB's Twin Trailer Study estimate that use of twins lowers LTL carrier costs by approximately 2 percent, or by about $500 million per year (TRB 1986, 109). Assuming that these savings are reduced by 5 percent because of access regulation, the cost to users of twins would be on the order of $25 million per year (0.05 x $500 million). Combining these estimates suggests that access regulation, because it reduces the productivity advantages of STAA vehicles, costs the primary users of STAA vehicles about $125 million, or about one fourth of 1 percent of their operating revenues (Roberts and Fauth 1988, 338), per year. Although this figure does not include many less quantifiable costs, such as the administrative cost to carriers and shippers of applying for access and costs associated with carrier uncertainty about equipment purchases and use, it provides a rough estimate of some of the major productivity losses associated with access regulation. SUMMARY ASSESSMENT Trucking companies have been rapidly integrating the longer and wider tractor-semitrailers and twin trailer trucks permitted by the STAA into their fleets. Yet, because the trucking industry is varied and different types of carriers have different equipment needs, these vehicles have not appealed equally to all segments of the trucking industry. Findings Carriers who specialize in hauling cargo in truckload lots are the primary users of the STAA tractor-semitrailers. TL carriers account for between 85 and 90 percent of combination truck traffic, including virtually all private carriage and the vast majority of for-hire truck travel. Because of its extra cargo space, the 48-ft trailer is becoming the TL industry stan-
90 PROVIDING ACCESS FOR LARGE TRUCKS dard. On the other hand, the use of twin trailer trucks has been concen- trated within the LTL segment of the industry. LTL carriers, who account for 10 to 15 percent of combination truck traffic, specialize in moving multiple shipments in a single truck. Twins offer productivity gains be- cause of their greater volume capacity and because dividing loads into smaller trailers reduces the number of times shipments must be handled and the number of trips required. However, because these advantages are not important to TL carriers, twins still account for only 5 to 6 percent of all combination truck mileage. The majority of the carriers and shippers interviewed for this study reported no or few serious problems resulting from access regulation. Because most states have adopted lenient regulations or enforcement policies, in practice STAA vehicles are allowed on virtually all roads. For some users of STAA equipment, however, access regulations, where they do exist, have presented problems. Carrier and shipper execu- tives noted the following problems: Inability to reach some locations, which forces some carriers to maintain additional fleets of non-STAA trucks, discontinue service to some established customers, or violate access limits; Circuitous routing and hours-of-service limits, which result in addi- tional truck miles and scheduling difficulties; and The time and paperwork burden of applying for access, which strains the administrative capacities of some smaller companies. Judging from the responses during interviews with the carriers and shippers, 5 percent might be a reasonable estimate of the share of trips by carriers of lightweight cargoes, the major beneficiaries of the more spa- cious STAA vehicles, that is adversely affected by access regulations. Assuming that access regulations result in increased travel using smaller and less efficient equipment (e.g., 45-ft trailers), the cost to carriers and shippers of lightweight cargoes would be about $125 million, or one fourth of 1 percent of their operating revenues, each year. Implications for Truck Access Policies The different uses made of STAA vehicles are important factors that explain carrier problems with many state access policies. Hence, well- designed access policies should be sensitive to the following findings:
STAA Vehicle Use and Productivity 91 Because many carriers travel to a wide variety of locations that are often far from the National Network, short access distance limits may be inadequate for access to terminals and other destinations, unless such access is coupled with extensive through-travel networks. Also, because many carriers must be responsive to the changing daily needs of shippers, it may be impractical for them to apply for permission for access in advance. Narrow and precise definitions of "terminal" can be troublesome to the vast majority of carriers who do not use their own facilities for handling freight but load and unload at many different shippers' and receivers' docks. Lists and maps of terminal access routes, because they are often outdated or do not show short access routes, may be inappropriate for carriers who operate over many different kinds of roads to many different locations. NOTES TL carriers normally pick up a full truckload shipment from one shipper and deliver it to one or more receivers. LTL carriers normally pick up many small shipments from several shippers, combine them into truckload lots for line haul, and deliver them to several receivers. These figures are rough approximations that include a large number of private companies with fleet sizes of five or fewer trucks and owner-operators who lease their services and equipment to larger carriers. In the case of small-package carriers (for example, United Parcel Service), ship- ments may weigh considerably less. Before passage of the Motor Carrier Act of 1980, many regulatory changes were already being made administratively within the ICC. In many ways this administra- tive deregulation stimulated and eased passage of the 1980 act (Derthick and Quirk 1985, 164-174). Of the 12 TL carriers interviewed, 8 were among the top 100 carriers of TL freight in 1987, and the remaining 4 were leading operators of more specialized refrig- erated and flatbed equipment. All 8 LTL carriers interviewed were among the top 50 LTL trucking companies in the country (Desmond 1988, 84-87). The network efficiencies and reduced freight handling resulting from the use of twins are important to normal LTL operations. To illustrate, LTL shipments transported in a standard tractor-semitrailer must be handled numerous times between the points of origin and destination. Twin trailer trucks offer an oppor- tunity to bypass some of these steps. For example, a standard tractor-semitrailer might arrive at an intermediate terminal in Charlotte, North Carolina, with part of its load headed for Atlanta and the remainder bound for Columbia, South Caro- lina. Before the use of twins, the shipments bound for Atlanta would be removed at
92 PROVIDING ACCESS FOR LARGE TRUCKS the intermediate terminal and loaded onto a tractor-semitrailer with other ship- ments to Atlanta. The space in the tractor-semitrailer bound for Columbia would then be filled with other shipments to Columbia. In contrast, a twin trailer truck arriving at the intermediate terminal in Charlotte would not require the handling needed for tractor-semitrailers. The shipments to Atlanta would initially have been loaded into one of the 28-ft trailers, and the shipments to Columbia would have been loaded into the other trailer; the trailers would simply be separated in Charlotte and coupled with other trailers headed for each respective destination. In addition, when the twin trailer trucks arrived at their inbound terminals, they would be decoupled and used for delivery instead of having their cargo unloaded onto smaller delivery trucks. Several carriers noted that Pennsylvania has recently improved its application procedures by reducing response time and the number of categories of STAA vehicles that is regulated. The in-depth interviews of carriers and shippers conducted for this study provide an overview of the range of problems related to access regulation and the resulting costs to individual carriers and shippers who can potentially benefit most from the widespread use of STAA equipment. Although the findings from such a small survey sample cannot be translated directly into industrywide estimates of access costs, they provide some basis for estimating a rough order of magnitude cost to major users of STAA vehicles. Because access problems are confined primarily to eastern states where 53-ft trailers are largely prohibited, the cost of access regulations to users of these vehicles is likely to be minimal. The carriers and shippers interviewed for this study generally did not report significant problems with access for 53-ft trailers per se, but emphasized their desire for more eastern states to legalize these vehicles. REFERENCES ABBREVIATIONS FHWA Federal Highway Administration TRB Transportation Research Board Census Bureau. 1984. Truck inventory and Use Survey 1982 (magnetic tape). U.S. Department of Commerce. Derthick, M.,and P. Quirk. 1985. The Politics of Deregulation. Brookings Institu- tion, Washington, D.C., 265 pp. Desmond, P. 1988. The Big Boys Crying Dereg Blues . . . All the Way to the Bank. Commercial Carrier Journal, July, pp. 83-88. Highway Statistics 1987. 1988. FHWA, U.S. Department of Transportation. Hoffman, K.C. 1988. Regional Niche Carriers Thrive by Sticking to Their Knit- ting. Traffic World, Oct. 17, pp. 12-14. Lane, L.L. 1988. Innovation in Trucking: Advanced Truckload Firms. In Trans- portátion Research Record 1154. TRB, National Research Council, Washing- ton, D.C., pp. 11-14. Murphy, J.V. 1988. End of Freight Rate Wars Raises Hope for Second Half. Traffic World, Oct. 17, pp. 6-10.
STAA Vehicle Use and Productivity 93 Office of Technology Assessment. 1988. Gearing Up for Safety. Congress of the United States, 188 pp. Roberts, P.O., and G.W. Fauth. 1988. The Outlook for Commercial Freight Transportation. In A Look Ahead: Year 2020. Special Report 220. TRB, National Research Council, Washington, D.C., pp. 329-353. Standley, 3., and M. Roman-Slavin. 1988. Industry Trends and Statistics. Com- mercial Carrier Journal, July,. pp. 97-118. Transportation Policy Associates. 1988. Transportation in America. Washington, D.C. TRB. 1986. Twin Trailer Trucks. Special Report 211. National Research Council, Washington D.C., 388 pp. TRB. 1987. Zero Alcohol and Other Options: Limits for Truck and Bu.c Drivers. Special Report 216. National Research Council, Washington, D.C., 196 pp. Trinc Transportation Consultants. 1983. Trinc's Blue Book of the Trucking Indu.s- try. Dun and Bradstreet Corporation, McLean, Va. Truck Trailer Manufacturers Association. 1988/1986. Van Trailer Size Report. Alexandria, Va.
5 Safety Accident Studies T HE SURFACE TRANSPORTATION ASSISTANCE ACT (STAA) of 1982 established safety as the primary criterion to guide the development of access policies for STAA vehicles on public roads within states. Thus a key issue in determining the extent of access that should be provided is how the accident experience of STAA vehicles compares with that of the vehicles they replace. As was discussed in Chapter 3, states differ widely in the criteria they use to determine where STAA vehicles can travel. These differences stem in part from inadequate and inconsistent information about the accident experience of longer and wider trucks. The purpose of this chapter is to examine the safety literature to provide answers to the following questions: What evidence is available for use in comparing the accident experi- ence of STAA vehicles with that of combination vehicles of pre-STAA dimensions? Do STAA vehicles have higher overall accident rates? higher accident severity rates? Are there differences in accident experience by STAA vehicle con- figuration? twin trailer trucks versus tractor-semitrailers? What evidence is available about differences in accident experience on different types of roads, particularly on non-Interstate highways that constitute the majority of access routes? These questions are addressed in this chapter. The discussion begins with an overview of the safety record of large combination vehicles' compared with that of passenger cars. Then, the safety literature is 95
96 PROVIDING ACCESS FOR LARGE TRUCKS reviewed to identify information relevant to each of the preceding ques- tions. Finally, the chapter concludes with a summary of the major findings about what is known, as well as what is not known, about the safety record of STAA vehicles. OVERVIEW OF COMBINATION VEHICLE SAFETY AND TRAVEL The reluctance of some state and local officials to broaden access for STAA vehicles stems, in part, from a general concern about the safe operation of all large combination vehicles in the traffic stream. Although some states, particularly in the East, had limited experience with vehicles of the dimensions authorized by the 1982 STAA before passage of the act, other large combination vehicles were commonplace in most states. Their accident performance and travel characteristics influenced the states' general perception of large-truck performance on the road. Combination Vehicle Involvement in Accidents and Accident Rates Combination vehicles are involved in a small portion of the total number of motor vehicle accidents reported each year. Of the 11,069,000 vehicles estimated to have been involved in accidents in 1986, the latest year for which national accident statistics are available, only 2.1 percent, or 235,000 vehicles, were combination trucks (Table 51).2 In comparison, nearly 75 percent of all accident-involved vehicles in 1986 were passenger cars (Table 5-1). When combination vehicles are involved in accidents, however, the accidents tend to be severe. Of the 60,755 vehicles involved in fatal accidents in 1986, 6.7 percent were combination vehicles and 60 percent were passenger cars (Table 5-1). The higher proportion of fatal combina- tion vehicle accident involvements relative to all combination vehicle accident involvements is explained in part by the differences in size and weight between large trucks and passenger cars. When large combination vehicles become involved in an accident, the accident is likely to be severe. A comparison of the accident involvements of combination vehicles and passenger cars does not take into account the relative amounts of travel of each type of vehicle and, thus, their relative accident risk. Two
Safety 97 vehicles may have the same number of accident involvements, but if one travels twice the distance of the other, its accident rate (i.e., number of accident involvements divided by miles traveled) is half that of the other. For accidents of all types, combination vehicles have slightly less than half the accident involvement rate of passenger cars (Table 5-2). However, the reverse is true for fatal accident involvements: combination vehicles have nearly twice the fatal accident involvement rate of passenger cars (Table 5-2). This ratio has declined slightly since 1982 (Figure 5-1). The higher fatal accident involvement rates of combination vehicles are explained in part by their different travel patterns, a topic that is discussed more fully in the next subsection. Sixty-five percent of combination vehicle travel is on rural highways where speeds are higher and accidents tend to be more severe; in comparison, 37 percent of passenger car travel is on rural roads (Highway Statistics 1987 1988, 171). TABLE 5-1 ACCIDENT INVOLVEMENTS BY ACCIDENT AND VEHICLE TYPE, 1986 [National Highway Traffic Safety Administration (NHTSA) 1988, x, 26, 36; NHTSA 1981-1988, 6-21 Fatal Accident All Accident Involvements Involvements No. Percentage No. Percentage Passenger cars 8,239,000 74.4 36,157 59.5 Combination 235,000 2.1 4,050 6.7 trucks All other motor 2,595,000 23.5 20,548 33.8 vehicles Total 11,069,000 100.0 60,755 100.0 TABLE 5-2 ACCIDENT INVOLVEMENT RATES BY ACCIDENT AND VEHICLE TYPE, 1986 (NHTSA 1988, x; NHTSA 1981-1988, 6-2; Highway Statistics 1987 1988, 171) vr Involvements/ Involvements (millions) 100 Million VMT All Accidents Passenger cars 8,239,000 1,301,214 633.0 Combination trucks 235,000 81,833 287.0 Fatal Accidents Passenger cars 36,157 1,301,214 22.8 Combination trucks 4,050 81,833 4.9 VMT = vehicle-miles traveled.
98 PROVIDING ACCESS FOR LARGE TRUCKS h C-) 0 4 1979 1980 1981 1982 1983 1984 1985 1986 YEAR Passenger Car8 M Combination Vehicles FIGURE 5-1 Fatal accident involvement rates by vehicle type, 1979-1986 (NHTSA 1979-1986, Highway Statistics 1979-1986). Combination Vehicle Travel Patterns and Accident Rates by Type of Road A National Truck Trip Information Survey conducted by the University of Michigan Transportation Research Institute (UMTRI) in 1986 (Campbell et al. 1988) provides a good picture of the travel patterns of large combi- nation vehicles in that year.3 Approximately three-fifths of all combina- tion vehicle travel is on divided highways (Campbell et al. 1988, 105). Major undivided highways carry one-third of all combination vehicle travel; only 8 percent of total mileage is on local roads. Major undivided highways include both four-lane undivided and two-lane highways, many of which are typical of access roads off the National Network. The travel patterns of combination vehicles differ by vehicle configura- tion. The tractor-semitrailer dominates combination vehicle travel, ac- counting for 92 percent of total miles traveled (Campbell et al. 1988, 82-83). Three-fifths of these miles are on divided highways. A somewhat greater share (three-fourths) of twin trailer truck travel is on divided highways (Campbell et al. 1988, 82-83); however, twins and other multi- ple-trailer combination vehicles accounted for only 5.5 percent of all combination vehicle travel at the time the travel survey was conducted. (The remaining 2.5 percent of combination vehicle travel is by straight trucks pulling a single trailer.) The fatal accident experience of combination vehicles varies dramati- cally as a function of the type of road traveled. Drawing from its compre- hensive data base , UMTRI found that fatal accident involvement rates for combination vehicles are highest on major undivided highways where
Safety 99 trucks can travel at high speeds and the opportunity for accidents is far greater than on divided highways. Accident rates are also high on local roads, but these account for only a small fraction of total combination vehicle travel. In comparison with the overall fatal accident involvement rate of 2.8 per 100 million vehicle-miles of combination truck travel, the fatal accident involvement rate is only half this value on divided highways, but it is approximately 80 and 45 percent higher on major undivided highways and local roads, respectively (Campbell et al. 1988, 105). Summary Combination vehicles are involved in a relatively small share of all motor vehicle accidents but in a higher share of fatal accidents. When differ- ences in travel by vehicle type are taken into account, combination vehicle accident involvement rates are lower than passenger car involvement rates for all accidents and higher for fatal accidents. These findings in part reflect the disparity in size and weight between combination vehicles and passenger cars, which increases the severity of truck-involved accidents. They also reflect the higher share of combination vehicle travel on rural roads where speeds are high and accidents tend to be more severe. According to a recent national survey of truck travel by UMTRI, approximately three-fifths of all combination vehicle travel is on divided highways, typical of the National Network, that are designed to the highest standards and have lower fatal accident involvement rates than other types of roads. Nearly one-third of combination vehicle travel is on major undivided highways, which are similar to truck access roads, and fatal accident involvement rates are higher on these roads than on divided highways. The issue is whether expanding access to STAA vehicles on major undivided highways will result in even higher accident involvement rates. In the following section an attempt is made to answer this question by reviewing the accident record of STAA vehicles relative to that of the vehicles they replace (i.e., mainly tractor-semitrailers with 40- and 45-ft trailers). COMPARATIVE ACCIDENT EXPERIENCEâ STAA VERSUS NON-STAA VEHICLES A review of the safety literature did not yield any studies that directly examined the accident record, either total accidents or fatal accidents, of STAA vehicles relative to vehicles of pre-STAA dimensions. This is not a surprising finding. First, national accident records are based on police
100 PROVIDING ACCESS FOR LARGE TRUCKS reports, which usually do not distinguish between the various dimensions of interest (i.e., 48- versus 45-ft semitrailers or 102- versus 96-in, vehicle width).5 Only 13 state highway and transportation departments,6 in the survey conducted for this study, reported that their accident records , distinguished between STAA and non-STAA vehicles, and the data are incomplete in six of these states.7 An additional six states indicated that these data would soon be available or could possibly be obtained by reprogramming existing data. The biggest problem is differentiating among various vehicle widths and lengths; differences in vehicle configu- rations (i.e., tractor-semitrailers versus twin trailer trucks) are more readily apparent. Second, even if greater detail were available, it would be difficult to make the case that these vehicle size differences were actually responsible for (i.e., caused) any identifiable difference in accident experience. Acci- dents are a function of many factors, including the handling and perfor- mance characteristics of the vehicles, the roadway design, the characteris- tics of the traffic on the roadway, the operating environment, and the driver. The relationships among these factors are not well understood and cannot readily be quantified, which complicates the task of isolating factors that contribute to increased accident risk. Vehicle Configuration and Accident Rates Several studies have examined differences in safety performance by vehi- cle configuration, focusing particularly on the comparative accident expe- rience of tractor-semitrailers and twin trailer trucks.8 Because twin trailer trucks were not allowed in many eastern states until passage of the 1982 STAA and because concerns for the safe operation of these vehicles have resulted in limited access for twins in many of these states, the findings of these studies are of interest. For its special study, Twin Trailer Trucks, the Transportation Research Board (TRB) conducted an extensive literature review of studies compar- ing the relative accident rates of twin trailer trucks and tractor-semi- trailers (TRB 1986, 127-133, Appendix F). The present review is focused mainly on studies that were published after the TRB report, but the findings of relevant earlier studies (Table 5-3) are also highlighted.9 Recent Studies In its Analysis of Accident Rates of Heavy-Duty Vehicles (Campbell et al. 1988), which drew from 5 years of national fatal accident data
Safety 101 (1980-1984) and the truck travel survey previously described, UMTRI analyzed fatal accident involvement rates for a variety of truck configura- tions and travel categories. The accident data base includes all medium and heavy trucks with a gross vehicle weight of more than 10,000 lb that were involved in a fatal accident in the 48 contiguous states and is probably the most complete national data base available on fatal truck accidents. The study found that when fatal accident involvement rates were analyzed by vehicle configuration, twin trailer trucks were slightly under- involved at 0.90 and tractor-semitrailers were slightly overinvolved at 1.06 in comparison with a normalized rate of 1.0 for all truck configurations. However, these results may reflect differences in truck travel by road class, time of day, and area (i.e., rural or urban) as well as differences in vehicle configuration. When the analysis was adjusted to control for these factors and isolate the effect of configuration, twin trailer trucks showed a 10 percent higher fatal accident involvement rate than did tractor-semi- trailers (Campbell et al. 1988, 40). The UMTRI study suffers from at least two potentially important limitations. First, as the authors point out, the 5 years of accident data (1980â 1984) are compared with only 1 year of travel data (1986) to derive the accident involvement rates (Campbell et al. 1988, 27). Because twin trailer truck travel, in particular, was growing rapidly during this period, use of the later year exposure data may cause accident involvement rates to be underestimated for twins in the earlier years. Second, it is impossi- ble to determine if the differences in fatal accident involvement rates are statistically significant on the basis of the data provided. A 2-year study conducted by Stein and Jones (1988) for the Insurance Institute for Highway Safety (IIHS) also investigated the relative safety of twin trailer trucks and tractor-semitrailers. Using a case-control meth- odology, the researchers analyzed all crashes on two Interstate highways in the state of Washington involving large trucks weighing more than 10,000 lb and resulting in personal injury or property damage of at least $1,500. Each crash-involved truck was matched with a control sample of three trucks selected randomly from the traffic stream at the same time of day and in the same location 1 week after the crash (Stein and Jones 1988, 492). The distribution of the crash-involved trucks was compared with that of the control sample trucks by vehicle configuration to determine relative involvement rates. It was found that twin trailer trucks were overinvolved in crashes by a factor of 2 to 3 regardless of accident type (i.e., single- versus multiple- vehicle crashes), truck operating and fleet characteristics (i.e., load, fleet size), driver characteristics (i.e., age, hours of service),and environmen- tal and road conditions (i.e., day or night, curve or grade) (Stein and
TABLE 5-3 SUMMARY OF STUDIES EXAMINING ACCIDENT RATES BY TRUCK CONFIGURATION Study Principal Finding Involvement Rate Ratio: Twins to Tractor-Semitrailers (by VMT) Base Data and Method Campbell et at. 1988 Twins have a 10 percent higher 1.10 1980-1984 UMTRI accident fatal accident involvement file; 1986 exposure data; me- rate than tractor-semitrailers dium and heavy trucks when accident rates are ad- > 10,000 lb justed for differences in travel by road class, time of day, and area Stein and Jones 1988 Twins are overinvolved in 2.00 to 3.00 Case-control methodology; crashes compared with trac- 1984-1986 large truck tor-semitrailers by a factor (>10,000 Ib) accidents and of two to three regardless of control sample on two Inter- accident type, truck operat- state highways in Washing- ing characteristics, driver ton characteristics, and environ- mental and road conditions Jovanis et al. 1988 Twins had lower accident in- Statistically less than 1.0 Matched-pair analysis; large volvement rates than tractor- LTL general freight carriers; semitrailers over a 3-year pe- 1983-1985 data nod and the differences were statistically significant for travel on Interstate, state, and local roads
TRB 1986 Twins are slightly overinvolved 0.98 to 1.12 Synthesis of prior studies for in truck crashes, but a pro- accident rates and indepen- jected 9 percent reduction in dent travel forecast truck travel from twins' greater capacity will offset any accident increase; no net Graf and Archuleta safety decrement Twins have higher accident in- 1.12 (rural roads) California data; 1979-1983 ac- 1985 volvement rates than tractor- 0.79 (urban roads) cident information and 1982 semitrailers on rural roads traffic counts and lower involvement rates on urban roads Glennon 1981 No statistically significant dif- 1.06 Pennsylvania data-1976 to ference in accident involve- 1980; matched pair analysis; ment between twins and large LTL general freight tractor-semitrailers . carriers Chira-Chavala and No statistically significant dif- 0.98 Bureau of Motor Carrier O'Day 1981 ference in accident involve- Safety 1977 accident data ment rates between twins and 1977 travel data from and tractor-semitrailers the Truck Inventory and Use Survey (U.S. Census); ICC- authorized carriers only Yoo et al. 1978 No statistically significant dif- 1.01 California data; 1974 accidents ference in accident involve- and travel counts ment rates between twins and tractor-semitrailers Data from multiple sites have been combined to compute the rates shown with weights equal to total (semitrailer plus multitrailer) mileage at each site (TRB 1986, 130 and Appendix F).
104 PROVIDING ACCESS FOR LARGE TRUCKS Jones 1988, 491) and that these differences were statistically significant. The difference was sufficiently large to offset any positive effects of projected decline in twins travel, which had been estimated in the TRB study, Twin Trailer Trucks, at 9 percent, resulting from the vehicle's greater cargo-handling capacity (Stein and Jones 1988, 497). A primary purpose of the case-control method, a widely used tech- nique in epidemiology, was to minimize the effects of the operating environment and time of day so that the effect of vehicle configuration, if any, could be more easily detected. The IIHS study, however, was the only study to find such a pronounced effect for vehicle configuration and little or no effect for such factors as crash type or time of day. Because the study results are extremely sensitive to the design of the control group and its representativeness of actual on-the-road truck traffic, the findings would have been strengthened by independent counts of truck traffic by vehicle type at the time of selection of the control vehicles. The extent to which the study results can be generalized is also an issue. Haddon et al., on whose research the IIHS methodology was patterned, caution that the results from this method are only valid for the locations examined because the case sites may not be typical of other locations (Haddon et al. 1961, 671, 675). Thus the IIHS study findings are only applicable to the Wash- ington Interstate routes studied until the results can be replicated nation- wide. A third recent study, presented at the 68th Annual Meeting of TRB, found, in contrast with the IIHS study, that tractor-semitrailers have consistently higher total accident rates than do twin trailer trucks on the Interstates, state highways, and local streets investigated and that these differences are statistically significant10 (Jovanis et al. 1988, 25). The study used industry data from national less-than-truckload (LTL) general freight carriers (Consolidated Freightways, Inc., and Yellow Freight System, Inc.) for a 3-year period, 1983 through 1985, for terminal routes that were used by both twin trailer trucks and 45-ft tractor-semi- trailers. The routes were located primarily in the East, Midwest, and South. Accident records and travel exposure were measured for ran- domly selected terminal pairs that served both twins and tractor-semi- trailers in an effort to control for differences in travel patterns and thereby isolate the effect of truck configuration as had the IIHS study. The controls, however, did not extend to time of day or driver characteristics (e.g., driver age, experience). The study results and their significance could have been affected by the researchers' elimination of routes with low travel volumes from the anal- ysis after the initial random selection of terminal pairs.'1 The results are also applicable only to the types of operations and carriers from which the
Safety 105 data derive, that is, large national LTL trucking firms conducting line- haul, general freight operations. The approach taken by the Jovanis study is modeled on an earlier effort by John Glennon to compare accident rates for twin trailer trucks and tractor-semitrailers by a matched pair analysis that controlled for differ- ences in travel characteristics. Using data on Pennsylvania, which were provided by Consolidated Freightways, Inc., Glennon randomly selected paired trips from a pooi of trips that occurred on the same date and over the same route (there were a minimum number of trips for each vehicle type) (Glennon 1981, Appendix B, 3)12 The trip records were further analyzed to ensure that there were no large variations between night and day and driver characteristics (e.g., experience, accident records) by vehicle configuration. No significant differences were found between the accident rates of twin trailer trucks and those of tractor-semitrailers (Glennon 1981, Appendix B, 4), and these results were used in litigation by Consolidated Freightways to protest Pennsylvania's restrictions on twin trailer truck operations. Earlier Studies TRB's Twin Trailer Trucks and the other methodologically sound studies reviewed in that report generally found either that twin trailer trucks were slightly overinvolved in truck crashes or that there were no statistically significant differences in the accident involvement rates of the two vehicle configurations (Table 5-3). Drawing on the findings of three key studies,13 the TRB report concluded that accident involvement rates for twin trailer trucks were slightly higher than for tractor-semitrailers, but that this slight decrement in safety would be offset by a projected 9 percent reduction in travel by twin trailer trucks attributable to the greater capacity of these larger trucks (TRB 1986, 155). The study concluded that, on balance, there would be no adverse safety impact from the operation of twin trailer trucks (TRB 1986, 155). Similar results were found in earlier studies. Chira-Chavala and O'Day found no overall difference in accident involvement rates between twin trailer trucks and tractor-semitrailers (1981, 3). The study was based on 1977 accident data from the Bureau of Motor Carrier Safety (BMCS) and exposure data from the Truck Inventory and Use Survey of the same year. The findings apply only to Interstate Commerce Commissionâauthorized carriers, because the BMCS data underreport the accident experience of private carriers. Chira-Chavala and O'Day, however, were quick to point out that the
106 PROVIDING ACCESS FOR LARGE TRUCKS characteristics, operation, and uses of twin trailer trucks and tractor- semitrailers are so different that a simple comparison of overall accident involvement rates would not provide an adequate explanation of their relative safety (Chira-Chavala and O'Day 1981, 12). This conclusion was confirmed by the UMTRI study in 1988. When factors such as trip length and trailer type were considered in a multivariate analysis of accident involvement rates, the effect of vehicle configuration on accident involve- ment rates, although significant, was overshadowed by the effects of the other two factors (Chira-Chavala and O'Day 1981, 74). Two studies, (Yoo et al. 1978 and Graf and Archuleta 1985) used California accident data to examine differences in total accident involve- ment rates between twin trailer trucks and tractor-semitrailers. The ear- lier study concluded that there were no statistically significant differences in accident involvement rates between the two configurations. However, if accident involvement rates were calculated on a ton-mile basis, twin trailer trucks had a lower accident involvement rate than did tractor- semitrailers (Yoo et al. 1978, 25). Graf and Archuleta also found no statistically significant differences in total accident involvement rates between twin trailer trucks and tractor- semitrailers (Graf and Archuleta 1985, 4), but when differences in oper- ating environment (i.e., rural and urban) were taken into account, twin trailer trucks had higher accident involvement rates on rural roads and lower accident involvement rates on urban roads (Graf and Archuleta 1985,5). Although the significance of these findings may be limited by the uncertainty of the travel estimates (particularly the urban area estimates) and the difficulty of generalizing the results beyond California because of the relatively unique use of twins in that state,14 the findings underscore the importance of looking beyond vehicle configuration to understand accident performance. Summary The majority of the studies just reviewed concluded that the differences in accident involvement rates between twin trailer trucks and tractor-semi- trailers are small; however, flaws in nearly all of the studies preclude a definitive assessment of the comparative accident record of the two vehicle configurations. The study findings fall short in at least two re- spects. First, calculation of exposure data is problematic in many of the studies and is central to their findings because, as has been shown, twin trailer trucks and tractor-semitrailers have very different travel patterns. Second, even when the studies attempt to control for differences in travel
Safety 107 characteristics, the study designs are such that the results cannot readily be extrapolated to a broad range of situations. For policy makers determining the extent to which STAA vehicles can operate safely off the National Network, the most important finding, on which the studies generally concur, is that vehicle configuration per se is less important in ascertaining the relative accident risk of these vehicles than are the types of roads on which and conditions under which they travel. This finding also holds if accident severity rather than total acci- dent involvement is examined. Vehicle Configuration and Severity of Accidents Accident severity is another major factor to consider in evaluating the accident performance of vehicles. Two vehicle types may have the same overall accident involvement rates, but one type may be involved more frequently in severe accidents, that is, in accidents that cause death or injury, and thus may be a greater hazard. Many of the studies that compared the relative accident experience of twin trailer trucks and tractor-semitrailers also addressed the issue of accident severity (Table 5-4). Some of the studies found higher fatal accident involvement rates for twins, and others found either no signifi- cant differences in accident severity between the two vehicle types or a mix of outcomes (e.g., twin trailer trucks showed higher fatal accident involvements but lower injury involvements than tractor-semitrailers). However, even those studies that showed higher fatal accident involve- ment rates for twins concurred that differences in the operating environ- ment were far more important in explaining the likelihood of involvement in a severe accident than were vehicle configuration, size, or weight. Vehicle operating environment has a profound effect on relative acci- dent severity. In his study, The Severity of Large Truck Accidents, Hed- lund found that accident location had a far greater effect on accident severity than did the size or weight of the truck (Hedlund 1977, 1). Using accident data from the 1973 and 1974 files of the BMCS, Hedlund measured accident severity as the incidence of car occupant fatalities in car-truck accidents.'5 Although he showed that, overall, twins were more likely to be involved in a severe accident than tractor-semitrailers, these differences became statistically insignificant when roadway type (i.e., two-lane, four-lane) and area (i.e., rural, residential/business) were taken into account (Hedlund 1977, 8). Two reasons for this finding were suggested: (a) rural accidents are more severe than accidents in residen- tial or business areas regardless of the type of truck involved and (b) twins
Vehicle involvement in fatal and injury accidents 1976-1981 BMCS accident files for five-axle trucks carrying general freight in van trailers (ICC-authorized carriers) TABLE 5-4 SUMMARY OF STUDIES EXAMINING ACCIDENT SEVERITY RATES BY TRUCK CONFIGURATION Study Principal Finding Carsten 1987 No statistically significant difference in fatal or injury involvements for twins and tractor-semitrailers; lack of differences attributed to greater use of twins on divided highways and higher involvement of twins in single- vehicle crashes TRB 1986 No statistically significant difference between twins and tractor-semitrailers in fatal accident involvements; twins are involved in fewer injury accidents and differences are statistically significant Accident Severity Measure Vehicle involvement in fatal and injury accidents Base Data and Method 1980-1982 UMTRI fatal accident file; 1981-1984 NASS injury file; and 1982 Truck Inventory and Use Survey
Fraction of accidents that result in fatalities and fraction of accidents that result in injury Incidence of a fatality to a car occupant in a car-truck accident BMCS 1977 accident data and 1977 travel data from the Truck Inventory and Use Survey; ICC-authorized carriers only 1973-1974 BMCS accident files for trucks > 13,000 lb and articulated trucks Vehicle involvement in fatal and California data; 1979-1983 casualty (i.e., fatal and injury) accident information and 1982 accidents - traffic counts Graf and Twins and tractor-semitrailers Archuleta have similar fatal accident 1985 . involvement rates on rural roads, but twins have fatal involvement rates more than double those of tractor- semitrailers on urban roads Chira-Chavala Twins are slightly more involved and O'Day in fatal accidents and slightly 1981 less involved in injury accidents Hedlund 1977 No statistically significant difference in fatality rates between twins and tractor- semitrailers when area and road type are taken into account
110 PROVIDING ACCESS FOR LARGE TRUCKS have a greater proportion of their accidents (i.e., 65 percent versus 51 percent) on rural roads. Thus, when these factors are controlled for, the remaining effect of vehicle configuration is quite small (Hedlund 1977,9). A study of the accident performance of twins and tractor-semitrailers in California (Graf and Archuleta 1985) arrived at a similar conclusion. The study found that fatal accident involvement rates overall for twins were nearly 25 percent greater than for tractor-semitrailers (Graf and Archu- leta 1985, 4). However, when accident involvement rates were examined by area, fatal accident involvement rates for twins were nearly the same as for tractor-semitrailers on rural roads, but more than twice the involve- ment rate for tractor-semitrailers on urban roads (Graf and Archuleta 1985, 4). Although the uncertainty of the estimates of travel on urban roads raises questions about the validity of the latter results, the findings nevertheless point out the importance of considering the operating envi- ronment in a comparative analysis of accident rates. Differences in accident severity between twin trailer trucks and tractor- semitrailers may also be explained by differences in the types of accidents experienced by these two vehicle configurations. A special analysis con- ducted for TRB (Twin Trailer Trucks, Appendix G) found that twins were involved in fewer injury accidents16 (statistically significant) and in fewer fatal accidents (not statistically significant) than would be expected if their accident involvement proportions were identical to those of tractor-semi- trailers (TRB 1986,337). Six years (1976-1981) of accident data from the BMCS were analyzed, focusing on five-axle trucks used by ICC-autho- rized carriers to carry general freight in van trailers. One reason given for the difference in accident performance between the two vehicle types was the different types of accidents they experience. A greater share of tractor-semitrailer crashes than of twins crashes involved multiple vehi- cles (59 percent versus 44 percent, respectively); these differences re- mained statistically significant in both rural and urban areas, in all geo- graphic regions, and for all highway types (TRB 1986, 339). Two other studies found similar effects. Carsten, in Safety Implications of Truck Configuration, reported no statistically significant difference in either fatal or injury accident involvement rates between twins and trac- tor-semitrailers (Carsten 1987, 20). Carsten based his analysis on accident data drawn from the UMTRI fatal accident file (1980-1982), the NHTSA National Accident Sampling System injury file (1981-1984), and expo- sure data from the 1982 Truck Inventory and Use Survey. He attributed the finding to differences between the environments in which the two types of vehicles operate and the types of accidents in which they are involved. He found, for example, that fatal accident involvement rates differed greatly by road type. Rural Interstates, on which twins travel most, showed the lowest fatal accident involvement rates (Carsten 1987,
Safety 111 21). Twins were also involved in a higher proportion of single-vehicle accidents. The author hypothesized that the overrepresentation of twins in single-vehicle accidents could be evidence of greater handling problems and found evidence in nonfatal accident involvement data of the higher propensity for rollover of the rear trailer unit of accident-involved twin trailer trucks. However, these handling problems did not result in higher fatal or injury accident involvement rates for twins relative to tractor- semitrailers (Carsten 1987, 26). Chira-Chavala and O'Day (1981) found that, overall, twins were in- volved in fewer crashes resulting in a casualty than were tractor-semi- trailers [i.e., twins were slightly more involved in fatal accidents and slightly less involved in injury accidents (Chira-Chavala and O'Day 1981, 81)]. They also noted that the difference may be attributed to differences in operating environment and accident type. Twins travel more on di- vided highways at night and are involved in a higher percentage of noncollision accidents17 than are tractor-semitrailers, 41 percent and 27 percent, respectively (Chira-Chavala and O'Day 1981, 5). Again, the safety literature does not provide a definitive answer regard- ing the relative severity of crashes involving twins versus tractor-semi- trailers. The studies concur, however, that understanding the environ- ment in which these vehicles operate is key to an assessment of their relative safety risk. The following section is an examination of what is known about the accident performance of twins and tractor-semitrailers on different types of highways, particularly non-Interstate highways, which are most likely to serve as access roads to service facilities and terminals. ACCIDENT EXPERIENCE BY ROAD TYPE AND CHARACTERISTICS What is known about combination vehicle, and where possible STAA vehicle, accident experience by road class is reviewed. The following issues are addressed: (a) Which roads have the worst accident record for large combination vehicles? (b) Do different vehicle types have different accident records on roads of similar classification? and (c) Are there special urban safety impacts that should be taken into consideration in determining the extent of access to be provided near large metropolitan areas? Also examined is the literature on highway conditions (e.g., nar- row lanes and shoulder widths) that pose the greatest danger of accident for all motor vehicles; that danger could be exacerbated by increased travel by combination vehicles.
112 PROVIDING ACCESS FOR LARGE TRUCKS Accident Rates by 'ilype of Road The studies that have examined large combination vehicle accidents by road type generally agree on the types of roads that are associated with the highest accident involvements. As previously discussed, the UMTRI study examined fatal accident involvement rates for combination vehicles on three classes of highways and found that the highest rates were on major undivided highways and the lowest rates on divided highways (Campbell et al. 1988, 105). When these road classes were further subdi- vided into rural and urban areas, major rural undivided highways exhib- ited the highest fatal accident involvement rates, followed by rural local roads (Figure 5-2). These higher fatal accident involvement rates were attributed to high travel speeds on and poorer design of many undivided highways, particularly major undivided highways (Campbell 1988, 3). Hedlund (1977) also found that truck accidents on two-lane rural roads were more likely to result in a fatality than were those on four-lane rural roads; truck accidents in residential and business areas were least likely to result in a fatality. The author attributed this finding to the increased likelihood of high-speed, head-on collisions on two-lane rural roads and other high-speed crashes on four-lane rural roads; low-speed crashes, with less severe effects, would likely predominate in residential and business areas (Hedland 1977, 7). (This type of information was not recorded in the BMCS file from which the accident data were gathered.) 2.5 2 LU 1 1.5 0.5 0 z DIR DIU MR MU LR LU FIGURE 5-2 Fatal accident involvement rates for combination vehicles by type of road and area (Campbell et al. 1988, 105); Di = divided highways, M = major undivided highways, L=local roads, R=rural, U=urban.
Safety 113 Graf and Archuleta (1985) found that large-truck (i.e., tractor-semi- trailer and twin trailer truck) accident involvement rates were substan- tially higher for all accidents, fatal accidents, and casualty (fatal and injury) accidents on nonfreeway routes (Graf and Archuleta 1985, 4). The results, however, are limited by the relatively small sample of non- freeway sites. When the results were analyzed by rural and urban roads to yield a better sample size, they showed that fatal accident involvements were higher on rural routes, but that total accident involvements and casualty involvements were higher on urban roads (Graf and Archuleta 1985, Attachment E). These findings suggest the effect of speed on the severity of truck accidents in rural areas. In a study of the factors that affect the severity of accidents involving combination vehicles (Chira-Chavala et al. 1984), road class was found to be particularly important. Undivided rural roads had the highest fatality ratio (i.e., the ratio of the number of fatal accidents to the number of nonfatal accidents), followed by divided rural roads and urban streets (Chira-Chavala et al. 1984, 26). However, little difference was reported in injury ratios (i.e., the ratio of the number of injury accidents to the number of property-damage-only accidents) among these three road types. In sum, researchers agree on a number of factors related to accident experience by road type. First and not unexpectedly, accident perfor- mance on undivided highways is much poorer than on divided highways, which are generally built to higher design standards. Second, total acci- dent involvement rates and fatal accident involvement rates for all combi- nation vehicles are highest on major undivided rural highways. The latter finding is attributed to the relatively high speed of travel on many of these rural roads and their poorer design, which increase the potential for accidents. Thus the risk of an accident becomes greater when large combination vehicles leave the National Network and particularly when they travel on undivided rural highways. However, these findings do not address the basic question of whether this accident risk is further in- creased by the introduction of STAA vehicles on these roads. An attempt is made to address this issue in the following subsection. Vehicle Configuration and Road Type Although a majority of studies have found that accident rates vary more by road type than by vehicle configuration, several of these studies have found some differences by vehicle type. Typically these differences are in overall vehicle configuration (i.e., twin trailer truck versus tractor-semi-
114 PROWDING ACCESS FOR LARGE TRUCKS trailer) rather than in any particular vehicle dimension (e.g., longer trailer lengths, wider vehicles). The UMTRI analysis, which compares fatal accident involvement rates by road type for two main vehicle configurations (Campbell 1988, 3, 6), shows that twin trailer trucks are nearly always safer than or as safe as tractor-semitrailers on all types of roads (Figure 53)â¢18 The exception is daytime travel on undivided rural roads (major undivided highways and local roads are combined in this analysis) where twins show a higher fatal accident involvement rate. This exception may reflect the existence of two twins populationsâthose that are used in line-haul operations by LTL carriers primarily on Interstate and other divided highways at night and those that are used in a few states as specialized carriers on local roads primarily during daytime hoursâor it may be an artifact of the data. Two additional studies (Chira-Chavala and O'Day 1981 and Graf and Archuleta 1985) found that twins generally have a better accident record than do tractor-semitrailers on non-Interstate undivided highways that are most similar to truck access roads. Chira-Chavala and O'Day focused on van trailers for both vehicle types and found that twins have a much D1DR DiDU D1NR DINU ODR ODU ONR ONU TRAVEL CATEGORY FIGURE 5-3 Fatal accident involvement rates by vehicle configuration, type of road, area, and time of day (Campbell 1988,6); Di = divided highways, 0 = major undivided highways and local roads, D=day, N=night, R=rural, U=urban.
Safety 115 lower total accident involvement rate than do tractor-semitrailers on local roads and an approximately equal accident involvement rate in intercity travel (Chira-Chavala and O'Day 1981, 73). The authors also found that twins are involved in a considerably smaller share of accidents resulting in casualties (i.e., they are involved in a higher share of accidents resulting in a fatality but in a lower share of accidents resulting in injury) in local travel (Chira-Chavala and O'Day 1981, 81). Graf, whose data are based on the accident experience of twins in California, also found that the total, fatal, and casualty accident involve- ment rates of these vehicles are lower than those of tractor-semitrailers on nonfreeways (Graf and Archuleta 1985, Attachment D). However, the nonfreeway results may be affected by the small sample size. These studies suggest that twin trailer trucks perform as well as or better than tractor-semitrailers on highways that are most similar to truck access roads. These results reflect the fact that, with the exception of a few states where twins are used for specialized hauling on local roads, travel of twins, and thus their accident involvement, is largely confined to Interstate and other divided highways. To the extent that travel of these vehicles is increased on non-Interstate undivided highways that are known to have higher accident involvement rates, their accident record could become worse. However, as the discussion in the next chapter indicates, the maneuverability of the articulated twin trailer truck on roadway curves and at intersections may provide twins with special advan- tages on local roads. Tractor-semitrailers, in comparison, have a poorer accident record on roads that are most similar to truck access routes. To the extent that the increased wheelbase length of the STAA tractor- semitrailers lessens their ability to negotiate roadway curves and intersec- tion turns, extending access for the longer STAA tractor-semitrailers could increase accident risk. Urban Safety Impacts Traffic congestion and the frequency of multiple-vehicle crashes in urban areas raise questions about the special impacts of expanding truck access in these areas. Only 3 of the 50 states that responded to the survey conducted for this studyâFlorida, Maine, and Rhode Islandâdifferenti- ated between urban and rural areas in setting mileage-based truck access limits. In these jurisdictions, STAA vehicles are allowed to travel farther off the National Network or state-designated networks in rural than in urban areas.
116 PROVIDING ACCESS FOR LARGE TRUCKS Several of the studies reviewed for this report shed light on the compar- ative accident experience of large combination vehicles in urban and rural settings. The UMTRI study of fatal accident involvement rates found that fatal accident involvements for all combination vehicles were higher on urban than on rural divided highways, but that the reverse was true on undivided highways, which areclosest in character to truck access routes (Campbell et al. 1988, 105). Graf and Archuleta's analysis of truck accidents in California (1985) also found that fatal accident involvement rates for combination vehicles were generally lower on urban than on rural roads, but that casualty and total accident involvements were higher (Graf and Archuleta 1985, At- tachment E). Chira-Chavala et al. (1984) confirmed these two studies' finding that fatality ratios for twin trailer trucks and tractor-semitrailers (van type) were lower on urban roads (Chira-Chavala et al. 1984, 26, 31 and TRB 1986, 335).19 However, they also found that, in multiple-vehicle accidents, injury ratios for tractor-semitrailers were higher on urban roads under most environmental conditions. Injury ratios for twins were typically higher on rural roads; these ratios were exceeded only by those for accidents under wet snowy conditions on urban roads (Chira-Chavala et al. 1984, 26, 31 and TRB 1986, 336). A review of the safety problems of large trucks in urban areas (O'Day and Kostyniuk 1985) examined the characteristics of urban truck acci- dents in an attempt to understand their special safety problems. Drawing on data on Texas, a state with relatively complete fatal and nonfatal accident records, the authors found that a higher proportion of urban accidents takes place on Interstate highways and that a higher proportion of urban crashes than of rural crashes involves multiple vehicles (O'Day and Kostyniuk 1985, 314-315). The authors' conclusion, however, that, all else being equal, increasing the proportion of large trucks in urban areas would result in increased fatalities and injuries (O'Day and Kos- tyniuk 1985, 316) is predicated on an expected increase in truck travel on urban Interstates and does not necessarily apply to access routes. The main conclusions of these studies that are germane to the question of extending access in urban areas are, first, that fatal accident involve- ments for combinations vehicles are lower on non-Interstate urban roads than on non-Interstate rural roads and, second, that injury accident involvements are generally higher on urban roads. (In the latter case, the studies do not distinguish between Interstate and non-Interstate high- ways.) The main reasons for these differences are the lower speeds on non-Interstate urban roads, which result in lower fatality rates, and the greater likelihood of multiple-vehicle crashes on congested urban roads,
Safety 117 which results in higher injury rates. The studies do not consider what effect substituting STAA vehicles for combination vehicles of pre-STAA dimensions would have on these accident rates. However, unless it can be argued that the STAA equipment generally handles and performs better than the equipment it replaces, extending access on urban roads for STAA vehicles is, at best, likely to have the same effect as increasing combination vehicle travel in general, that is, to increase injury accident involvements but not fatal accident involvements. To the extent that commodities can be handled more efficiently in the larger STAA equip- ment, thereby reducing the number of trips required to handle a given quantity of cargo, these effects can be reduced, but the net impact is unknown. Roadway Characteristics and Accident Experience A significant number of studies have addressed the relationship between specific highway design features (as opposed to road class) and motor vehicle accidents. The committee that prepared Designing Safer Roads: Practices for Resurfacing, Restoration, and Rehabilitation reviewed exist- ing research results and commissioned new research to quantify the relationships between improvements in highway design and accident reduction (TRB 1987, 78). The major findings of this effort are reviewed here to identify the design features of access roads that may present the greatest hazards for motor vehicle travel. Two limitations of the studies should be kept in mind. First, most of the safety relationships are applicable only to two-lane rural roads because the majority of the prior research focused on rural highways; thus urban highway design features are not specifically addressed. Second, the studies are primarily concerned with passenger vehicles. Where possible, the relevance of the findings for large combination vehicles, and more specifically for STAA vehicles, is noted. At least six highway design features identified in the TRB study may have significant bearing on the accident experience of STAA vehicles traveling on access roads: Lane and shoulder width and type, Bridge width, Roadsides and sideslopes, Pavement edge drops, Horizontal curves, and Intersections.
118 PRovIDING ACCESS FOR LARGE TRUCKS The increase in combination vehicle width from 96 to 102 in. is clearly linked to the first and second featuresâthe adequacy of lane and shoulder width and shoulder type and bridge width. The increase in vehicle length, particularly the attendant problems of trailer encroachment onto op- posing traffic lanes or shoulders or curbs at curves and intersections as a result of offtracking20 (see discussion in Chapter 6) of the longer-wheel- base STAA tractor-semitrailers, is related to the remaining four features. What is known about the impact of each of these features on the safety of motor vehicle travel is summarized in the following subsections; particu- lar emphasis is placed on large combination vehicle travel. Lane and Shoulder Width and Shoulder Type Approximately 60 percent of rural highway fatalities that are caused by single-vehicle, head-on, and sideswipe accidents are affected by lane and shoulder conditions (TRB 1987, 81). Adequate lane width is important to provide sufficient lateral separation between vehicles to avert sideswipe and head-on collisions of vehicles that are passing or meeting on two-lane roads. Adequate lateral separation is more important for cars meeting or passing trucks, particularly the wider combination vehicles authorized by the STAA. Adequate shoulder width is also important to increase the opportunity for safe recovery when vehicles run off the road. Because large combination vehicles have a higher incidence of single-vehicle acci- dents than do passenger cars [i.e., 34 percent of multiunit truck accidents are single-vehicle crashes versus 17 percent for passenger vehicles (NHTSA 1988a, 25,36)], adequate shoulder width is critical. Finally, the type of shoulder is important for safe truck operation because of the offtracking problems of longer-wheelbase STAA tractor-semitrailers and the likelihood of rollover if the truck wheels leave the pavement edge (stabilized shoulders alleviate these problems). The research findings indicate that increasing lane and shoulder width can reduce the risk of certain types of accidents. However, pavement widening, per foot of added width, has a greater accident risk reduction payoff than does shoulder widening, and stabilized shoulders reduce accidents more than unstabilized shoulders (TRB 1987, 81-83). For example, widening lanes from 9 to 12 ft without any shoulder improve- ments is projected to reduce accidents by as much as 32 percent for all types of vehicles. Adding 3 ft of unstabilized shoulder where there was none is projected to reduce accidents by 19 percent, and adding 3 ft of stabilized shoulder increases the projected reduction to 22 percent (TRB 1987, 81-83). The benefits of widening, however, are not linear. For
Safety 119 example, the largest benefit is achieved by the first foot of lane widening (Zegeer et al. 1987, 153). To the extent that width is a critical factor for cars passing trucks or trucks passing trucks, a topic that is discussed in the next chapter, narrow lane widths and narrow and unstabilized shoulders could pose a safety problem for STAA vehicles. Bridge Width Bridges can pose significant hazards. Research studies have identified bridge width as a principal factor affecting bridge safety: the greater the difference between the clear bridge width, which includes the traffic lanes and usable shoulders on the bridge structure, and the width of the approach lanes, the greater the number of accidents (TRB 1987, 87). Accident risk is further exacerbated when bridge approaches are on a downward grade, which can increase vehicle speed, and are sharply curved, which is frequently the case with older structures. Narrow bridges may pose a greater problem for large trucks than for passenger cars. The width of STAA vehicles and offtracking of the longer STAA tractor- semitrailers on sharply curved bridge approaches may pose particular problems on narrow bridges. Increasing the width of the bridge relative to the width of the approach lanes can reduce accidents by an estimated 40 percent (TRB 1987, 87). However, a large share of the safety gains, nearly one-third, is captured in the first foot of widening. Roadsides, Sideslopes, and Pavement Edge Drops Approximately 30 percent of accidents on two-lane rural roads involve single vehicles running off the road. Because combination vehicles are more likely to be involved in single-vehicle accidents than are passenger cars, adequate recovery areas at the road edge that are smooth, flat or without steep sideslopes, and clear of fixed objects are important to truck safety. Special research conducted for a TRB study indicated that there is a significant relationship between roadside recovery distance and accident rates; it was projected that increasing clear recovery areas would reduce the number of accidents (TRB 1987, 85). Correcting pavement edge drops, that is, vertical discontinuities at the edge of the paved surface, may also have important safety ramifications.
120 PROVIDING ACCESS FOR LARGE TRUCKS The longer-wheelbase tractor-semitrailers are particularly susceptible to edge drops on the inside of horizontal curves because of the inward offtracking of the rear wheels of the truck (TRB 1987, 97). However, existing information is inadequate for quantifying the benefits of correc- tive measures in terms of expected accident reductions. Horizontal Alignment Accidents are more likely to occur on curved than straight segments of roads because of the added demands placed on the driver to negotiate the curve and because of the behavior of the vehicle in the curve. Research suggests a linear relationship between degree of curvature and relative accident rates such that each degree of decrease in curvature results, on average, in three fewer accidents for every 100 million vehicles passing through the curve (TRB 1987, 91). Sharp curves are typically found in areas with topographic constraints, which result in roadway designs with narrow lane widths and limited shoulders, and are often accompanied by steep grades; these design features are known to contribute to roadside encroachments. Improvement projects are likely to address many of these related problems and thus result in additional benefits. Combination vehicles, especially the longer-wheelbase tractor-semi- trailers authorized by the 1982 STAA, have particular difficulty negotiat- ing sharp curves because of offtracking problems and the probability of rollover if the vehicle moves onto the shoulder. Thus the presence of sharp horizontal curves on rural access roads may increase the risk of rollover accidents. Intersections A substantial share of accidents occurs at intersections-55 percent of urban accidents and 32 percent of rural accidents (Accident Facts 1987, 50). Twenty-eight percent of the fatal accidents that take place on urban highways and 15 percent of those that take place on rural highways are intersection related (Accident Facts 1987, 50). The longer-wheelbase STAA tractor-semitrailers have greater difficulty negotiating many inter- section turns than do passenger cars or shorter-wheelbase tractor-semi- trailers because of offtracking problems. However, the number of acci- dents caused by offtracking is unknown, and predicting whether
Safety 121 intersection improvements will reduce accidents is difficult because so many factors, such as sight distance, number of lanes, lane width, traffic volume, and traffic signalization, affect the safety of turns at intersections (TRB 1987, 95). To the extent that inadequacies in the highway features just described are present on access roads, they have been shown to have measurable adverse effects on safety. Each of these features is associated with high accident levels for all types of motor vehicles. Because of their handling and performance characteristics and sheer size, combination vehicles, especially STAA vehicles, tend to have greater difficulty than do pas- senger cars in these settings. Although data are not available to provide direct evidence of the safety impacts in terms of increased accident rates, an increase in accident risk could be expected. SUMMARY AND FINDINGS Combination vehicles, as a class, are involved in a relatively small share of all motor vehicle accidents but in a higher share of all fatal accidents. These findings reflect the disparity in size and weight between combina- tion vehicles and passenger cars, which increases the severity of truck- involved accidents, as well as the greater share of combination vehicle travel on rural roads where high speeds contribute to accident severity. Fatal and total accident involvement rates are higher for combination vehicles traveling on major undivided four-lane and two-lane highways, which are most similar to truck access roads. The key questions that are addressed in this chapter are (a) whether STAA vehicles are more dan- gerous than the vehicles they replace, that is, whether their presence on the road will result in more total accident involvements or more fatal accident involvements, or both, and (b) whether STAA vehicles will perform more poorly on certain types of highways, particularly non- Interstate highways that are typical of access roads. Not surprisingly, a review of safety studies did not uncover any research that has directly compared the accident experience of STAA with non- STAA vehicles. However, several studies have examined the relative safety records of different vehicle configurations in an effort to compare the performance of the more controversial twin trailer truck with that of the more common tractor-semitrailer. Nearly all of these studies found that the difference in accident involvement rates between the two vehicle configurations is small. However, many of the studies have problems in estimating vehicle travel, which is central to calculating accident rates,
122 PROVIDING ACCESS FOR LARGE TRUCKS and most have enough methodological flaws of one type or another to make it difficult to reach a definitive assessment. This finding also holds for studies that examined accident severity by vehicle configuration. The studies generally concur, however, that vehicle configuration per se is less important in determining relative accident risk than are the types of roads on which these vehicles travel and the environments in which they operate. When accident experience is examined by road type, research results show that undivided highways are less safe for combination vehicle travel than are divided highways and that major undivided rural highways have the highest total accident and fatal accident involvement rates for combi- nation vehicles. The latter finding is attributed to the poorer design of and the high speed of travel on many rural highwaysâcharacteristics that increase the potential for accidents and accident severity. The accident experience of twin trailer trucks and tractor-semitrailers differs, however, by road type. Twins generally have accident involve- ment rates that are lower than or the same as those of tractor-semitrailers on undivided highways, which are most similar to access roads. Tractor- semitrailers, in contrast, have a poorer accident record than do twins on these roads. The safety impact of expanding truck access in urban areas is unknown. Studies find that fatal accident involvement rates for combination vehicles are lower and injury accident involvement rates higher on urban than on rural roads. The main reasons for these differences are lower speeds on urban roads, which reduce fatality rates, and greater probability of multi- ple-vehicle crashes on urban roads, which increases the likelihood of injury. Unless the case can be made that STAA vehicles generally handle significantly better than the vehicles they replace, it is likely that extend- ing access on urban roads for STAA vehicles would have the same effect as extending access for combination vehicles in general, that is, to increase injury accident involvements but not fatal accident involvements. To the extent that the larger, more efficient equipment can reduce the number of trips required to carry a given quantity of freight, these adverse effects would be reduced, but the net safety impact cannot be quantified. Certain highway features of two-lane rural roads have been associated with high accident levels for all types of motor vehicles. Because combina- tion vehicles, particularly STAA vehicles, may have greater difficulty than passenger cars in these settings, these conditions may increase the risk of accidents. The effect of restrictive geometric features of roadways on the performance of STAA vehicles, compared with their effect on the perfor- mance of vehicles of pre-STAA dimensions, is examined in the next chapter.
Safety 123 NOTES Combination trucks include truck tractor-semitrailers, truck-full trailer combina- tions, multiple-trailer combinations (i.e., doubles and triples), and bobtail truck tractors (i.e., tractors not pulling a trailer). National accident statistics are based on a sample of accidents whereas fatal accident statistics are based on a census of all fatal accidents and thus should be more reliable. Although the trip information was collected in 1986, the vehicle sample was drawn from 1983 state registration files maintained by R. L. Polk (Campbell et al. 1988, 11). Fatal accident involvements were drawn from a special file created by UMTRI that combines data in the NHTSA Fatal Accident Reporting System and data collected by the Office of Motor Carriers (formerly known as the Bureau of Motor Carrier Safety) of the Federal Highway Administration. Follow-up calls were made to obtain missing data. The accident data were then pooled for 1982, 1983, and 1984 to provide the results given here. The UMTRI fatal accident file can distinguish between the dimensions of interest but there are twolimitations of the data base. First, it only includes fatal accident involvements, and, second, because fatal accidents are infrequent events, accident and exposure data for several years must be pooled to provide an adequate sample size for comparing fatal accident rates for different vehicle sizes. Arkansas, Colorado, the District of Columbia, Florida, Illinois, Maryland, Min- nesota, North Carolina, North Dakota, South Carolina, South Dakota, Vermont, and Virginia. Three states cannot distinguish STAA length dimensions and one state cannot distinguish width. Accident records were only available for Interstate highways in one state, and the accident records of another state were not available in a usable format. Twin trailer trucks, although not necessarily of the larger dimensions authorized by the 1982 STAA, have been in operation in many states for a long enough period to establish a reliable accident record for comparative purposes. Because of the obvious difference between a tractor-semitrailer and a twin trailer truck, this difference is likely to be recorded accurately on police accident report forms. Not all studies have been included. For example, a 1988 study by G. Sparks et al., The Safety Experience of Large Trucks In Saskatchewan, which examined differ- ences in the accident experience of twin trailer trucks and tractor-semitrailers in western Canada, was not reviewed because no attempt was made to control for the different usage patterns of the two vehicle types, which the authors believed to account for the observed difference in overall accident rates. The data on local routes should be used with caution, however, because a portion of the local mileage was imputed for each terminal trip investigated (i.e., 2-mi access on local routes was assumed at the beginning and end of each trip between terminals). After the routes were initially screened, terminal pairs with fewer than 100 dispatches per year for each vehicle configuration were eliminated to avoid the problem of assigning equal weight to heavily traveled routes and routes with a small number of dispatches, and thus low travel mileage, which would tend to inflate accident rates.
124 PROVIDING ACCESS FOR LARGE TRUCKS Seven trips was the minimum number that could be used and still yield a sample of at least 100 million miles for each vehicle type, which had been determined a priori as an adequate travel volume. The studies were by Graf and Archuleta 1985, Chira-Chavala and O'Day 1981, and Glennon 1981. 141 In the majority of states, LTL carriers use twin trailer trucks to carry general freight. In California, however, twins are also used for specialized purposes, such as hauling agricultural products, dirt and gravel, petroleum products, and lumber. Each car-truck accident was classified as having either no car occupant fatalities or at least one such fatality, thereby removing the effect of a few extremely severe accidents (Hedlund 1977, 3). Accident severity was measured as the fraction of all reported accidents that resulted in injury and the fraction that resulted in death (TRB 1986, 337). 'Noncollision accidents often involve going off the road and overturning and thus are serious accidents. The authors caution, however, that small sample sizes invalidate the results for nighttime travel on undivided highways in rural and urban areas. The exception is single-vehicle accidents of twins, which have higher fatality ratios on urban roads. Fatality ratio is defined as the ratio of the number of fatal accidents to the number of nonfatal accidents. Offtracking is the phenomenon that occurs when the path of each rearward tire of a turning truck does not coincide with that of the corresponding forward tire with the result that the vehicle cannot stay within its proper lane. At low speeds, the rear wheels of the trailer track inward of the front wheels. REFERENCES ABBREVIATIONS Caltrans California Department of Transportation FHWA Federal Highway Administration NHTSA National Highway Traffic Safety Administration TRB Transportation Research Board Accident Facts. 1987. National Safety Council, Chicago, Ill. Campbell, K. L. 1988. Presentation to the MVMA/DOT Motor Truck Research Symposium on the Center for National Truck Statistics. The University of Michigan Transportation Research Institute, Ann Arbor, July 7. Campbell, K. L., D. F. Blower, R. G. Gattis, and A. C. Wolfe. 1988. Analysis of Accident Rates of Heavy-Duty Vehicles. DTNH22-83-C-07188. The University of Michigan Transportation Research Institute, Ann Arbor, April, 123 pp. Carsten, 0. 1987. Safety Implications of Truck Configuration. In Transportation Research Record 1111. TRB, National Research Council, Washington, D.C., pp. 17-26. Chira-Chavala, T., and J. O'Day. 1981. A Comparison ofAccident Characteristics and Rates for Combination Vehicles with One or Two Trailers. UM-HSRI-81-41. Highway Safety Research Institute, The University of Michigan, Ann Arbor, Aug.
Safety 125 Chira-Chavala, T., D. E. Cleveland, and L. P. Kostyniuk. 1984. Severity of Large-Truck and Combination-Vehicle Accidents in Over-the-Road Service: A Discrete Multivariate Analysis. In Transportation Research Record 975. TRB, National Research Council, Washington, D.C., pp. 23-36. Glennon, J. C. 1981. Matched Pair Analysis. Consolidated Freightways v. Lar- son, 81-1230 [reported in 647 F. Supp. 1479 (M.D. Pa. 1986)]. Graf, V. D., and K. Archuleta. 1985. Truck Accidents by Classification. FHWA/ CAITE-85. Caltrans, Sacramento; FHWA, U.S. Department of Transporta- tion, Jan., 20 pp. Haddon, W., P. Valien, J. R. McCarroll, and C. J. Umberger. 1961. A Con- trolled Investigation of the Characteristics of Adult Pedestrians Fatally Injured by Motor Vehicles in Manhattan. Journal of Chronic Diseases, Vol. 14, No. 6, Dec., pp. 655-678. Hedlund, J. 1977. The Severity of Large Truck Accidents. DOT HS-802-332; NHTSA Technical Note. U.S. Department of Transportation, April, 34 pp. Highway Statistics 1979-1 987. 1980-1988. FHWA, U.S. Department of Trans- portation. Jovanis, P. P., H. Chang, and I. Zabaneh. 1988. A Comparison of Accident Rates for Two Truck Configurations. Presented at 68th Annual Meeting of TRB, Washington, D.C., Jan. 1989, 29 pp. NHTSA. 1981-1988. Fatal Accident Reporting System 1979-1 986. DOT HS-807-254. U.S. Department of Transportation. NHTSA. 1988. National Accident Sampling System-i 986. DOT HS-807-296. U.S. Department of Transportation, July. O'Day, J., and L. P. Kostyniuk. 1985. Large Trucks in Urban Areas: A Safety Problem. Journal of Transportation Engineering (American Society of Civil Engineers), Vol. 3, No. 3, May, pp. 303-317. Sparks, G., J. Bielka, A. Smith, D. Marzolf, and R. Neudorf. 1988. The Safety Experience of Large Trucks in Saskatchewan. Saskatchewan Highways and Transportation, Regina; Transport Canada, Ottawa, 145 pp. Stein, H. S., and I. S. Jones. 1988. Crash Involvement of Large Trucks by Configuration: A Case-Control Study. American Journal of Public Health, Vol. 78, No. 5, May, pp. 491-498. TRB. 1986. Twin Trailer Trucks. Special Report 211. National Research Council, Washington, D.C., 388 pp. TRB. 1987. Designing Safer Roads: Practices for Resurfacing, Restoration, and Rehabilitation. Special Report 214. National Research Council, Washington, D.C., 319 pp. Yoo, C. S., M. L. Reiss, and H. W. McGee. 1978. Comparison of California Accident Rates for Single and Double Tractor-Trailer Combination Trucks. FHWA-RD-78-94. BioTechnology, Inc., Falls Church, Va.; FHWA, U.S. De- partment of Transportation, March, 70 pp. Zegeer, C. V., J. Hummer, D. Reinfurt, L. Herf, and W. Hunter. 1987. Safety Effects of Cross-Section Design for Two-Lane Roads. Final Report FHWA- RD-87/008. Goodell-Givas, Inc., Southfield, Mich.; FHWA, U.S. Depart- ment of Transportation, Oct., Vol. 1, 207 pp.
Highway Design and Accident Risk MAJOR FACTOR IN SELECTING APPROPRIATE ROADS for access is the adequacy of geometric design features of high- ways to accommodate the longer and wider STAA vehicles. Many roads on which access is sought were not built to the design standards of the Interstate system or other designated highways on the National Network. Thus it is important to understand how STAA vehicles handle and perform on roads with more restrictive geometry. The purpose of this chapter is to Identify the key geometric design features that may pose problems for STAA vehicle travel on access roads; Review the literature to summarize what is known about the rela- tionship between the operating characteristics of STAA vehicles and each of the geometric features; Identify the vehicle characteristics and geometric conditions that pose the most serious problems for STAA vehicles relative to the vehicles they replace; and Draw implications for developing access policies. Safety is the primary consideration in examining the relationship be- tween highway design and the performance and handling characteristics of STAA vehicles. However, as was indicated in the previous chapter, it is difficult to establish more than a general correlation between restrictive highway geometry and increased accident rates, much less between re- strictive geometry and the operation of specific types of vehicles. The approach taken here is more indirect. It focuses on highway design 127
128 PROVIDING ACCESS FOR LARGE TRUCKS features that are likely to increase accident risk for STAA vehicles, given their particular handling and performance characteristics, relative to the vehicles they replace. IMPORTANT GEOMETRIC FEATURES The key geometric features that may pose problems for STAA vehicle travel can be grouped into three categories: Alignment features âSight distance for passing and stopping âSlope and length of vertical grades âHorizontal curvature Cross-sectional features âLane widths âShoulder widths âRoadside design features Intersection, interchange, and ramp design elements âTurns and sight distance at intersections âSight distance at railroad-highway grade crossings âInterchange and ramp design Guidelines for each of these design elements have been established by the American Association of State Highway and Transportation Officials (AASHTO) and recently revised in A Policy on Geometric Design of Highways and Streets (AASHTO 1984). The federal government has adopted most of these policies as standards or design guides for Federal- Aid highways (Design Standards for Highways, Code of Federal Regula- tions, Title 23, Part 625), and state and local highway engineers generally rely on AASHTO policies as the standard design reference. AASHTO's 1984 geometric policy guide, however, was essentially com- plete before the 1982 STAA was enacted and thus did not fully take into account the vehicles authorized by the act or even the then more common tractor-semitrailer with a 45-ft trailer. Vehicle widths of 102 in. as mandat- ed by the 1982 STAA were included, but the longest vehicles were the WB-50, a tractor-semitrailer 55 ft in overall length with a 40-ft semitrailer, and the WB-60, a twin trailer truck 65 ft in overall length with two 27-ft trailers (AASHTO 1984, 21). The STAA of 1982 required states to permit tractor-semitrailers with trailer lengths of up to 48 ft (25 states have legal grandfathered trailer
Highway Design 129 lengths that range from 50 to 59.5 ft) and twin trailer lengths of up to 28 ft per trailer on the National Network and highways providing access to service facilities and terminals; overall length limits were abolished for vehicles traveling on these roads. Thus AASHTO design vehicles do not include the longer trailer lengths typical of STAA trucks, the operation of which is affected by such geometric features as roadway and shoulder width on curves, intersection turns, interchanges, and ramps. Before the 1982 STAA, the AASHTO design vehicles, the WB-50 and WB-60, represented the "worst case" vehicles from the perspective of geometric design and thus may not always have been used as design vehicles in the construction or rehabilitation of existing highways that are being consid- ered as access roads to and from the National Network. AASHTO is revising its 1984 policy guidelines and adding several new design vehicles, including tractor-semitrailers with 48- and 53-ft trailers.1 Guidance will be provided on how these new design vehicles affect curve and intersection pavement width and intersection sight distance require- ments. Incorporating STAA vehicles into the geometric design standards, however, is not a trivial task. First, the dimensions specified by the 1982 act are not sufficient to describe a vehicle for the purpose of design. Features such as tractor wheelbase and kingpin-to-rear-axle distance, which are neither specified nor controlled by the 1982 STAA, have a significant influence on geometric design. Second, because of the elimina- tion of overall vehicle length limits and the range of trailer lengths that are legal in different states, it is difficult to adequately define "generic" STAA vehicles for the purposes of geometric design. In evaluating current design policies as they relate to STAA vehicles, it should be kept in mind that few public highways are designed to fully accommodate the "worst case" design vehicle. For cost-effectiveness reasons, the AASHTO design policies are geared to the more common vehicles and tolerate some vehicle movements that exceed design values. States may modify these policies when traffic volumes and particular vehicle-operating problems warrant a more stringent approach, but states, too, are constrained by financial limitations. The surveys of the states conducted for this study indicated that 15 states have some informa- tion about the geometric improvements, such as lane widening and up- grading of intersections, needed to accommodate STAA vehicles on proposed or existing access roads; 17 states have actually modified their geometric design practices to accommodate STAA vehicle travel on their highways and have incorporated these modified design guidelines in new construction and improvement projects.2 Most local governments are not likely to have the staff or expertise to modify their design practices.
130 PROVIDING ACCESS FOR LARGE TRUCKS RELATIONSHIP BETWEEN STAA VEHICLE OPERATING CHARACTERISTICS AND HIGHWAY GEOMETRIC FEATURES Although AASHTO's Policy on Geometric Design of Highways and Streets does not fully address the problems of designing highways to accommodate STAA vehicles, several studies have examined their impact on highway geometry. The adequacy of geometric design guides is af- fected by the characteristics and performance of STAA vehicles, includ- ing minimum turning radius, offtracking, length, width, braking, and weight-to-power ratio [Transportation Research Board (TRB) 1986, 179]. What is known about the operating characteristics of STAA vehicles and how these interact with each of the key geometric features of interest is summarized in the following subsections. Sight Distance for Passing and Stopping Large combination vehicles may affect the adequacy of sight distance for passing and stopping because of their greater vehicle length and accelerat- ing and braking characteristics. Passing Adequate passing sight distance is a major concern on two-lane roads on which vehicles must use a lane that is traveled by vehicles in the opposing traffic flow to overtake a slower-moving vehicle. Passing sight distance is the distance needed to safely complete a passing maneuver (AASHTO 1984, 148). This distance is computed by adding the following factors: (a) initial maneuver distance; (b) distance traveled in the left lane by the passing vehicle; (c) distance at the end of the passing maneuver between the passing vehicle and the opposing vehicle; and (d) distance traversed by the opposing vehicle (Gericke and Walton 1981, 15). Current AASHTO design standards are predicated on the assumption that the vehicle passed is a passenger car. The greater length of STAA vehicles will have an effect on Factors b and d in the calculation of adequate passing sight distance for a passenger car passing a truck. Assuming the overtaken vehicle is a twin trailer truck 70 ft long and a passing speed differential of 10 mph, the passing car requires approximately 5.5 sec more to negotiate the passing maneuver-3.5 sec more in the left lane for the passing vehicle and 2 sec more for the
Highway Design 131 oncoming vehicle (Fancher 1986, 31). At a passing speed of 60 mph [corresponding to a design speed of 65 mph (AASHTO 1984, 155)] and considering the distance traveled by the oncoming vehicle, the required passing sight distance is increased by about 740 ft, nearly a one-third increase over the current 2,300-ft design practice recommended by AASHTO and a threefold increase over the 1,000-ft criterion adopted by the Manual on Uniform Traffic Control Devices (MUTCD) (Gericke and Walton 1981, 4). However, compared with passing a combination truck typical of pre-STAA dimensions (i.e., 60-ft overall length), passing the 10-ft-longer STAA twin trailer truck would require only 1/2 sec more time. Thus passing sight distance requirements are only slightly greater for a passenger car passing an STAA vehicle than for the same car passing a non-STAA vehicle, but both may be inadequate. Some investigators of alternative methods of computing passing sight distance requirements of large trucks on two-lane highways (Harwood and Glennon 1989) have recently argued that lower requirements for trucks could be adequate. Determining the adequacy of the AASHTO and the MUTCD passing sight distance criteria is beyond the scope of this study. However, even if the longer AASHTO-recommended passing sight distance requirements are accepted, there are mitigating factors. In calcu- lating total sight distances, AASHTO is conservative in estimating the initial maneuver distance; at a 60-mph passing speed, the driver of a passenger car has approximately 350 ft, or 4 sec, during which to abort the decision to pass.4 The decision may be affected, however, by drivers' inability to discriminate between trucks of various lengths, which may cause them to proceed without being cognizant of the increased time required to pass a longer STAA vehicle. Research on the effect of trucks on highway traffic on two-lane roads in Australia found that the distribu- tion of accepted distances for passing was independent of the length of the overtaken vehicle, which suggests that drivers cannot discriminate be- tween trucks of various lengths (Troutbeck 1984, 14-17). The MUTCD criteria are of greater concern because they are used as the basis for marking no-passing zones on two-lane highways. These criteria are based only on passenger cars and thus are inadequate for passenger cars passing not only twin trailer trucks but most other large combination vehicles as well. However, the MUTCD criteria are recog- nized as minimum operating criteria and there is no evidence in the safety literature that the current standards are a significant safety problem. Moreover, safety problems could be created if the standards for marking no-passing zones were based on a worst-case design vehicle, a large combination truck; faced with sharply reduced passing opportunities, drivers might simply ignore no-passing zone signs altogether. That cur-
132 PRovIDING ACCESS FOR LARGE TRUCKS rent practices for marking no-passing zones on two-lane roads with high volumes of truck traffic are inadequate for any large combination vehicle should be kept in mind when these roads are evaluated for access. Vehicle width was found to have a less significant effect than vehicle length on passing behavior of passenger cars and thus on passing sight distance requirements. A recent study of truck width and passing behav- ior found that there were no significant differences in passing time, distance, or speed for passenger vehicles passing trucks of widths varying from 96 to 114 in. (Seguin et al. 1982, 47). However, the study found that differences in accepted and rejected distances for passing decreased with increasing truck width, suggesting that drivers had a more difficult time determining the distance needed to pass wider trucks. There was no evidence, though, that passenger vehicle drivers accepted smaller dis- tances, and thus an increased accident risk, as truck width increased (Seguin et al. 1982, 14). The study did observe an increase in the head- ways of passing vehicles following a truck as truck width increased, suggesting a loss of sight distance associated with increased truck width. However, the additional passing distance resulting from this increase in initial headway for a 102-in, truck relative to a 96-in, truck is only 7 ft or /8 sec for a passenger vehicle traveling at 60 mph; the difference was statis- tically insignificant (Seguin et al. 1982, 14). In the case of an STAA vehicle passing another STAA vehicle, vehicle length as well as the acceleration capability of the passing truck affect sight distance requirements. The passing truck will spend longer in the left lane than a passenger car to clear the passed truck, and the passing maneuver will take longer because of the poorer acceleration rate and longer length of trucks relative to passenger cars (Hall 1986, 158). Two factors, however, help mitigate the problems introduced by a truck pass- ing another truck. First, the additional eye height of truck drivers may increase their sight distance relative to that of passenger vehicle drivers, particularly on vertical curves that are typical of two-lane rural roads. Fancher shows that in many cases drivers of trucks have 160 percent of the sight distance of drivers of passenger cars on vertical curves (Fancher 1986, 32). Truck drivers have no advantage, however, when sight distance is limited by horizontal curvature. Second, there is evidence to suggest that the weight-to-power ratios (gross vehicle weight divided by net horsepower) of large trucks, for gross weights up to 80,000 lb, are declin- ing because of increases in engine horsepower (Gillespie 1986, 77). As- suming that these trends continue, improvements in engine horsepower are likely to mitigate reductions in acceleration ability attributable to the slightly higher average weights of STAA vehicles. Because the passing of a STAA vehicle by another STAA vehicle on a two-lane road is likely to be
Highway Design 133 a relatively rare and random event, it is not generally appropriate to design for this situation. Stopping Minimum stopping sight distance is the distance required to stop a vehicle traveling at or near the design speed of a highway before it strikes a stationary object in its path. The adequacy of stopping sight distance is a function of vehicle speed, perception and reaction time of the driver, driver eye height, object height, braking performance of the vehicle, and road surface friction (TRB 1986, 378). AASHTO design values for mini- mum stopping sight distances are based on passenger cars and their braking characteristics. Minimum stopping distances for large trucks are substantially longer than those required by AASHTO policy. For example, the controlled deceleration of a truck traveling at 55 mph requires the same braking distance, approximately 800 ft, that is required for a passenger car travel- ing at 80 mph (Fancher 1986, 34). These calculations assume poor road- way conditions, wet weather, worn tires, and truck braking efficiency of less than 100 percent. However, if the higher eye height of truck drivers is taken into account, the minimum stopping sight distance differential is reduced to 10 mph (i.e., a large truck traveling at 67 mph will be able to make a controlled stop on a vertical curve designed for an automobile traveling at 80mph) (Fancher 1986, 34). Thus drivers of large trucks are at a moderate disadvantage relative to drivers of passenger cars on vertical curves and at a greater disadvantage on horizontal curves on which their higher eye height is not a help. However, these disadvantages should be similar for drivers of both STAA and non-STAA vehicles. Slope and Length of Vertical Grades Large trucks perform more poorly on upgrades than do passenger cars. They cannot maintain prevailing traffic speeds and thus may induce drivers of passenger cars to attempt potentially unsafe passing maneuvers on two-lane roads without climbing lanes. The speed loss of large trucks is primarily attributable to the physical characteristics of these vehicles, such as gross vehicle weight and weight-to-power ratio (Safwat and Wal- ton 1986, 64). AASHTO design policies recommend maximum grade lengths based on the WB-50 truck with a weight-to-power ratio of 300 1b- hp. Because STAA vehicles have at least as good a weight-to-power ratio
134 PROVIDING ACCESS FOR LARGE TRUCKS as the WB-50, STAA vehicles should not pose additional problems on grades on roads designed to current AASHTO design policies (Hall 1986, 160). Horizontal Curvature Large trucks may pose a significant problem on narrow two-lane roads with sharp curves. Two operating characteristics of large trucks cause particular problems. First, drivers of large trucks may experience diffi- culty in steering their vehicles in the center of the lane (AASHTO 1984, 236). Second, long trucks occupy more of the roadway when they are negotiating curves than do passenger cars because of offtracking or lateral displacement of the rear portion of the trailer (see Appendix E for a more detailed discussion of offtracking.) Offtracking is the phenomenon that occurs when the path of each rearward tire of a turning truck does not coincide with that of the corre- sponding forward tire, with the result that the vehicle may not be able to stay within its proper lane (Figure 6-1)--either the front of the vehicle swings into opposing lanes of traffic or the rear wheels run off the roadway (TRB 1986, 270 and Guide for Monitoring and Enhancing Safety on the National Truck Network 1986, 8). Extent of offtracking is a function of the geometry of the curveâshorter radii and larger turn angles increase the amount of offtrackingâand the dimensions of the vehicleâthe longer the wheelbase and the fewer the articulation points, all else being equal, the greater the offtracking (Guide for Monitoring and Enhancing Safety on the National Truck Network 1986, 10). The most significant vehicle dimen- sion for a tractor-semitrailer is the distance from the kingpin to the center of the rear axle or axles.6 From the perspective of highway design, the most relevant measure of the effect of vehicle offtracking is the swept path width, that is, the width of roadway the vehicle occupies in negotiating a curve or turn (i.e., the amount of offtracking plus the width of the vehicle) (Figure 6-1). For this reason AASHTO recommends that a truck be used as the design vehicle for determining needed pavement widening on curves. Because differences in the offtracking of most types of large trucks at design speeds over 40 mph and on turn radii larger than 400 ft are insignificant, AASHTO bases its calculations on a single-unit, 102-in. truck and suggests that adjustments be made where sharper curves and larger combination vehicles are prevalent (AASHTO 1984, 238). Special computer tabulations developed for this study7 (see Appendix E) indicate that the offtracking of the longer-wheelbase STAA tractor- semitrailers is greater than that of any of AASHTO's design trucks or of
Path of Fra Outside Tr Swept Pall Offtracklng Highway Design 135 FIGURE 6-1 Swept path width and offtracking of a truck negotiating a 90- degree turn (Caltrans). the 45-ft tractor-semitrailer that was common before the 1982 STAA. The offtracking performance of the STAA twin trailer truck, however, is equivalent to that of the WB-50 and slightly better than that of the 45-ft tractor-semitrailer. Table 6-1 gives the swept path width of six different design vehicles on a 90-degree turn with a 60-ft turn radius as an illustra- tion of these relationships. Because of offtracking, additional pavement width may be required on two-lane roads with sharp curves and high volumes of STAA tractor- semitrailer traffic. Table 6-2 gives the swept path, or pavement width, requirements of several design vehicles on roadway section curves with varying turn angles and turn radii. The data in the table indicate that
136 PROVIDING ACCESS FOR LARGE TRUCKS TABLE 6-1 COMPARISON OF MAXIMUM SWEPT PATH WIDTHS OF DESIGN VEHICLES ON 90-DEGREE TURN, 60-FT RADIUS Kingpin-to-Center- of-Rear-Axle Dimension Maximum Swept Path Vehicle Configuration (ft) (ft) 37-ft semitrailer, conven- tional cab (WB-50) 30.0 18 45-ft semitrailer, conven- tional cab 37.5 21 STAA twin trailer, cab over engine 22.5 17 48-ft semitrailer, conven- tional cab 40.5 22 53-ft semitrailer, conven- tional cab 45.5 25 59-ft semitrailer, conven- tional cab 51.5 28 NOTE: All tractors, except the twin trailer truck as noted, have 18-ft wheelbases. Itis assumed that rear trailer axles are in the farthest back position and vehicle width is 91 in. (see Appendix E). STAA tractor-semitrailers with conventional cabs require from less than 1.0 ft (for the 48-ft semitrailer) to approximately 3 ft (for the 59-ft semitrailer) more pavement than do the 45-ft semitrailers in common use before the 1982 STAA, assuming the rear trailer axles are in the farthest back position. The data suggest that a minimum radius of from 200 to 250 ft on roadway section curves is needed to contain the 48-ft tractor- semitrailers within a 12-ft lane width, and that from 250 to 300 ft are needed for the 53-ft tractor-semitrailer. The focus on offtracking as a particular problem of the longer-wheel- base STAA tractor-semitrailers assumes restrictive geometric conditions that limit highway speeds to below 40 mph. However, there may be situations in which STAA vehicles can attain higher speeds on curving two-lane roads. At high speeds, the lateral acceleration of the vehicle as it negotiates a curve creates a dynamic effect that causes the rear wheels of the vehicle to track outward from the front wheels, which could more than offset the effects of the inward offtracking that occurs at low speeds (personal communication with D. W. Harwood and W. D. Glauz, Mid- west Research Institute, January 26, 1989). High-speed or negative -off- tracking, which is a greater problem for the articulated twin trailer truck than for the tractor-semitrailer, is relatively small, typically no greater than about 1.4 ft (TRB 1986, 271, 272). After this point rear trailer rollover becomes the greater concern. Because of the low rollover thresh-
TABLE 6-2 MAXIMUM SWEPT PATH WIDTHS THROUGH ROADWAY SECTION CURVES Vehicle Configuration Turn Angle =30 Degrees and TR = 200 ft 250 ft 300 ft 400 ft Turn Angle = 60 Degrees and TR = 200 ft 250 ft 300 ft 400 ft 37-ft semitrailer, conventional cab (WB-50) 10.4 9.9 - 9.6 - 10.8 10 9.6 - 45-ft semitrailer, conventional cab 11.3 11 10.3 - 12 11.2 10.5 - STAA twin trailer, cab over engine 10.5 10 9.6 - 10.6 10 9.6 - STAA twin trailer, conventional cab 10.5 10 9.6 - 10.6 10 9.6 - 48-ft semitrailer, conventional cab 11.8 11.2 10.6 - 12.6 11.5 10.9 - 48-ft semitrailer, California cab 11.9 11.3 10.8 10.1 12.8 11.8 11.0 10.1 53-ft semitrailer, conventional cab 12.6 11.8 11.3 NA 13.6 12.5 11.7 NA 59-ft semitrailer, conventional cab 13.6 12.7 12.2 11.2 14.8 13.6 12.6 11.3 NOTE: Units are feet. Assumes vehicle width of 91 in. and rear trailer axles in the farthest back position (see Appendix E). California cab has a tractor wheelbase length of 20 ft. Dash = no change from lower turn radius; NA = not available; TR = turn radius.
138 PROVIDING ACCESS FOR LARGE TRUCKS old of large trucks, oversteering sharp horizontal curves at high speeds can increase the likelihood of rollover for both twin trailer trucks and tractor-semitrailers, a subject that is discussed at greater length in the subsection on interchange and ramp design. Under certain circumstances, the rear trailer of a twin trailer truck is more susceptible to rollover than the single trailer of a tractor-semitrailer unit. The driver of a multitrailer unit equipped with a single drawbar dolly may be unable to sense the instability of the rear trailer because the coupling mechanism is unable to effectively transmit roll moments from one unit to the next. Thus driver control over the rear trailer is reduced. The rear trailer can also become unstable in a maneuver involving rapid steering, such as avoiding an obstacle or a sudden lane change, which can lead to the rear trailer rolling over. In this case, the trailing unit experi- ences a higher lateral acceleration than the towing unit; lateral accelera- tion is amplified toward the rear of the vehicle, causing whiplike motion of the rear trailer (Winkler et al. 1987, 2). This rearward amplification is not observed in tractor-semitrailers. New technology is available to improve the lateral stability of the rear trailer of a twin trailer unit. When twin trailers are connected by a rigid "B-train" configuration, which essentially eliminates the articulation point between the two trailers and reduces the likelihood of rear trailer rollover, the stability of the rear trailer is greater than when twin trailers of the same length are connected by a conventional dolly (Ervin et al. 1986a, 143). Because B-dollies are heavier and more costly to buy and maintain than conventional dollies and reduce the flexibility of interchanging trailers, they are not yet in widespread use in the United States; research is being undertaken by the U.S. Department of Transportation on ways of improving truck control and stability through dolly design (Winkler et al. 1987). Lane Widths Clearance between meeting or passing vehicles and between vehicles and the edge of the pavement is a critical factor in determining the adequacy of pavement widths (Whiteside et al. 1973). These factors are, in turn, affected by vehicle width. AASHTO design vehicles have a width of 102 in. and thus take into account the size increase mandated by the STAA of 1982. AASHTO recommends a 12-ft lane width for comfortable clearance between com- mercial vehicles on major highways (AASHTO 1984, 360). Lane widths of lift are acceptable on two-lane rural highways that carry moderate volumes of mixed traffic and in urban areas where right-of-way and
Highway Design 139 existing development are stringent controls. Ten-foot lanes are acceptable only on low-volume, low-speed roads; lane widths less than 10 ft do not provide adequate lateral separation between commercial vehicles. Minimum lane width requirements for the safe operation of STAA 102- in. combination vehicles are a critical issue in the development of access policies. Seguin et al. examined the effects of truck width on the lateral separation and placement of vehicles passing a wide truck and on on- coming vehicles in the adjacent lane. Field tests were conducted on a straight two-lane highway with lane widths of between 10.5 and 12 ft and shoulder widths of 9 ft, of which 3 ft were paved (Seguin et al. 1982, 33). Traffic levels were low to moderate, with 15 to 20 percent commercial traffic, and speed limits were 55 mph. Truck widths on the experimental vehicle were varied from 96 to 114 in. Test results indicated that increasing truck width led to a reduction in both lateral separation and placement of the vehicles (Seguin et al. 1982, 13). When the lateral location of the driver's side of the truck was held constant while truck width was increased, the oncoming driver moved closer to the pavement edge, suggesting some intimidation effect (Seguin et al. 1982, 9). Even with the widest truck (114 in.), however, lateral separation between vehicles was still 4.0 to 4.5 ft. Although passing and oncoming vehicles moved closer to the pavement edge, only 6 percent encroached onto the shoulder. The researchers concluded that, although drivers interacting with trucks did respond differently as truck width increased, no major adverse impact on safety was observed, particularly for the smaller truck width increases (i.e., from 96 to 102 in.) (Seguin et al. 1982, 14). The authors acknowledged, however, that other possible effects of truck configuration on lateral separation, such as the tendency of truck trailers to sway horizontally, were not examined. Although there appear to be no definitive guidelines for appropriate lane widths for STAA vehicles, two observations can be made. First, the modest increase of 6 in. in vehicle width does not appear to have intro- duced any significant decrement in the safe operation of trucks on the highways. Second, minimum lane widths of lift, and even wider on roads with sharp curves, appear to be desirable on roads with high volumes of commercial traffic, whether the trucks be 96 or 102 in. wide. Shoulder Widths Shoulder widths clearly affect safe vehicle travel, particularly on narrow roads with commercial traffic where the driver of the truck or of the oncoming vehicle is likely to approach the pavement edge or encroach on the shoulder to provide adequate clearance.
140 PROVIDING ACCESS FOR LARGE TRUCKS AASHTO recommends shoulder widths of between 10 and 12 ft for heavily traveled, high-speed highways and of between 6 and 8 ft on lower- volume roads (AASHTO 1984, 365). Where lane widths are narrow, curves are sharp, and truck traffic volume is high, shoulders should have the same load-carrying capacity as the traveled way because trucks may encroach on the shoulder to maintain comfortable lateral distances from oncoming traffic and negotiate curves without encroaching onto the oncoming traffic lane (Guide for Monitoring and Enhancing Safety on the National Truck Network 1986, 22). On unpaved shoulders, the danger of truck rollover increases as the truck's right tires leave the roadway and come into contact with uneven surfaces. Because of the offtracking prob- lems of STAA tractor-semitrailers, and their greater potential for en- croaching on shoulders on curves, shoulder width and composition are likely to be of somewhat greater concern for STAA tractor-semitrailers than for the vehicles they replace. Roadside Design Features During the past 20 years, increasing attention has been devoted to provid- ing a roadside that is reasonably safe for vehicles that leave the roadway. Although design vehicles for most of these improvements have been passenger cars and light trucks, some roadside treatments will work with large trucks. For example, breakaway sign supports will break away when struck by a truck, although the sign itself will often be at windshield height. Other features pose problems not only for STAA vehicles but also for the WB-50. With their narrow track width and high centers of gravity, these vehicles are likely to overturn on sideslopes of 4:1 that can be safely traversed by passenger vehicles. Crash attenuators, which are used at points where fixed objects cannot be removed, will safely decelerate vehicles as heavy as 4,500 lb, but they will not work for 80,000-lb vehicles. Likewise, roadside barriers, including guardrails, concrete median bar- riers, and bridge rails, will safely contain and redirect passenger vehicles but not heavy trucks with high centers of gravity. The Texas Transporta- tion Institute (Hirsh 1986) has created some innovative designs to per- form these functions for trucks, but financial constraints will limit their application to only the most critical locations (e.g., where one major roadway passes over another). Overall, it does not appear that STAA vehicles are significantly more likely to run off the road, or create other problems, than are 'WE-SOs. Nevertheless, because most roadside fea- tures are not designed for either type of truck, they may warrant special consideration in the specification of access roads.
Highway Design 141 Intersection Design Intersections constructed to current AASHTO design guidelines pose at least two problems for STAA vehicles: (a) inadequate lane width for negotiating intersection turns without lane encroachment and (b) inade- quate sight distance for clearing the intersection. Intersection Turns Turning roadways should be designed to accommodate vehicle width plus an additional allowance for offtracking (TRB 1986,377). AASHTO bases its intersection design guidelines on the turning characteristics of the WB-50 (37-ft trailer) as the largest design vehicle. However, the offtrack- ing problems of the longer-wheelbase STAA tractor-semitrailers suggest that intersections built to current AASHTO design guidelines are inade- quate to accommodate these trucks. Because many intersections on ac- cess roads have been constructed to standards that are lower than those of the 1984 AASHTO Guide, they will be even less able to accommodate these trucks. In general, offtracking is greatest at low speeds when the rear wheels of the vehicle track inward of the front wheels. Using an offtracking equa- tion developed by the Western Highway Institute, Hall shows that the STAA 48-ft tractor-semitrailer exhibits substantially greater offtracking than the WB-50, particularly for short radii typical of right-hand turns (and left-hand turns on one-way street systems) (Figure 62).8 Thus curb radii and turning roadways that are designed to the minimum require- ments of the WB-50 will not be adequate for the longer STAA tractor- semitrailer (Hall 1986, 162). The computer tabulations prepared for this study were also used in examining the problem of offtracking at intersections with turn angles ranging from 60 to 120 degrees (Table 6-3). The results show that, as is the case for roadway curves, the STAA twin trailer truck requires no more pavement width than the WB-50 and less than the pre-STAA 45-ft trac- tor-semitrailer. However, the 48- and 53-ft tractor-semitrailers require between 19 and 28 ft of pavement to negotiate right turns at intersections with a turn radius of 60 ft, 3 to 9 ft more than the WB-50 (Table 6-3). The computer model, however, may overstate to some extent the amount of additional pavement width that is needed for trucks to negotiate turns without encroaching on. other lanes (Appendix E). Truck drivers nor- mally make adjustments in approaching intersection turns, such as mov- ing to the approach lane farthest from the curb at the beginning of the
142 PROVIDING AccEss FOR LARGE TRUCKS 28 26 22 U WB-50 1982 STAA Semi 20 18 16 14 12 10 8 30 50 70 90 110 130 150 170 190 RADIUS (feet) FIGURE 6-2 Comparison of maximum offtracking characteristics of the WB-50 and the 48-ft STAA tractor-semitrailer (Hall 1986, 162). turn to clear the curb, which reduces lane encroachment by between 3 and 6 ft on curves ranging from 60 to 120 degrees, assuming a 60-ft turn radius (Hummer et al. 1988, Tables 1 and 2). The Wisconsin Department of Transportation is studying the turning behavior of large trucks at intersections of two-lane roads in urban areas (DeCabooter and Solberg 1989). The purpose of the research is to exam- ine the functioning of large trucks at intersections that are geometrically inadequate, according to ideal turning templates, in order to differentiate intersections at which compensatory measures taken by truck and auto- mobile drivers can successfully overcome submarginal geometric configu- rations from intersections that are so seriously deficient that truck travel will create a safety problem. The results of the research to date indicate that, subject to traffic volumes, right-turning trucks (i.e., the worst case condition) can negotiate turns by taking advantage of gaps in the oncom- ing traffic on the intersecting roadway as long as the approach roadway is sufficiently wide to physically accommodate long trucks making the turn- ing maneuver (DeCabooter and Solberg 1989, 12). The researchers esti- mate that curb-to-curb approach street widths should be at least 40 ft
TABLE 6-3 MAXIMUM SWEPT PATH WIDTHS THROUGH INTERSECTION CURVES Vehicle Configuration Turn Angle = 60 Degrees and TR = 50 ft 60 ft Turn Angle = 90 Degrees and TR = 50 ft 60 ft Turn Angle = 120 Degrees and TR = 50 ft 60 ft 37-ft semitrailer, conventional cab (WB-50) 17 16 19 18 21 19 45-ft semitrailer, conventional cab 19.8 18.6 23 21.3 - 23 STAA twin trailer, cab over engine 16.8 156.8 18.8 17.0 20 18.0 STAA twin trailer, conventional cab 17 16 19.6 17.8 21 18.6 48-ft semitrailer, conventional cab 20.4 19.2 24.3 22 - 24.4 48-ft semitrailer, California cab 21.0 19.6 - 23 - - 53-ft semitrailer, conventional cab 21.7 20.9 26.8 24.8 30.8 27.8 59-ft semitrailer, conventional cab 24.6 23.2 30.2 27.9 35.6 32.0 NoTE: Units are feet. Assumes vehicle width of 91 in. and rear trailer axles in the farthest back position (Appendix E). California cab has a tractor wheelbase length of 20 ft. Dash = no change from lower turn radius; TR = turn radius.
144 PROVIDING ACCESS FOR LARGE TRUCKS (including parking lanes) to accommodate a 48-ft tractor-semitrailer with a trailer wheelbase length of 41 ft (DeCabooter and Solberg 1989, 24). This means that the truck would use a full 12-ft traffic lane plus an 8.5-ft parking lane on the approach roadway to begin the turn and the full curb- to-curb width of the intersecting roadway to complete the turn (Figure 6-3). Off tracking of a tractor-semitrailer can also be controlled by changes in the configuration of the vehicle itself. The distance from the kingpin to the center of the rear axle or axles is the critical dimension, although very long tractor lengths can also affect offtracking (see Appendix E). At a 90- degree intersection turn with a 60-ft turn radius, every 1-ft reduction in distance from the kingpin to the center of the rear axle reduces offtrack- ing by approximately three-fifths of a foot (Table 6-1). Truck drivers often shorten the distance from the kingpin to the center of the rear axle or axles by sliding the rear trailer axles forward to improve vehicle maneu- verability on local streets, and several states regulate wheelbase dimen- sions as a condition for granting access for tractor-semitrailers on local roads (see Chapter 3). Shortening the kingpin-to-rear-axle dimension should improve vehicle maneuverability but will also increase the overhang of the trailer on long tractor-semitrailer units. For example, a 53-ft semitrailer with a 41-ft kingpin-to-center-of-rear-axle setting would have 5 more feet of overhang than a 48-ft semitrailer with the same kingpin setting. The overhang becomes a problem in a rear-end collision in which a car strikes a truck. Because of the height differential between the car and the truck, the car can slide under (i.e., underride) the truck, a maneuver which is likely to cause fatalities to the occupants of the car. (If the truck strikes the car, the truck is likely to climb over the car, a phenomenon called override.) The Federal Highway Administration, as part of its Motor Carrier Safety Regulations, requires underride guards on large trucks but does not specify the required strength or height of the guard. The National Highway Traffic Safety Administration (NHTSA) has proposed a more stringent federal standard for underride guards on heavy trucks (i.e., greater than 10,000 lb) but has never issued the final rule. Alternatives to underride guards, such as better illumination of the sides and rear of trucks to help prevent collisions, are being considered. One state, Michi- gan, has authorized the use of 53-ft tractor-semitrailers with a 40.5-ft kingpin setting, measured from the kingpin to the center of the rear tandem axle assembly, on designated highways, but these vehicles are legal only if they have rear underride guards that meet state specifica- tions. In summary, the findings presented here indicate that the longer-
N1'L 1 IEâ 41 âal I e.S PRRURC I? LABS - TTCUI. o,aoec SCTRACU FROM CURBS B⢠FIGURE 6-3 Truck offtracking and encroachment on intersections of varying curb-to-curb width (DeCabooter and Solberg 1989, 25): left, offtracking and encroachment for approach 50 ft wide (note room available for opposing traffic to bypass encroaching trucks); right, offtracking and encroachment for approach 41 ft wide (trucks must either ride up on inside curb or use full approach width to complete turns).
146 PROVIDING ACCESS FOR LARGE TRUCKS wheelbase STAA tractor-semitrailers are likely to present problems at many urban intersections, particularly those built to or below minimum AASHTO design requirements. However, the amount of upgrading re- quired to accommodate STAA vehicles will vary as a function of the traffic volume, the composition of the traffic (i.e., the amount of STAA tractor- semitrailer traffic), and an assessment of the seriousness of the safety and traffic operating problems associated with these conditions. At intersec- tions, because of the relatively low speed of the traffic, the main effects of offtracking STAA tractor-semitrailers are likely to be reduced intersec- tion capacity and traffic flow, not a severe hazard. Mitigative measures, such as regulating vehicle wheelbase dimensions, can help reduce off- tracking, but, in some cases, physical limitations may necessitate recon- struction to accommodate STAA tractor-semitrailer traffic. Sight Distance at Intersections Sufficient sight distance should be provided at intersections for approach- ing vehicles to slow and stop if necessary, and for stopped vehicles to cross the intersection or make turns. Stopping sight distance was examined earlier, so this discussion focuses on the adequacy of sight distance for large trucks crossing or turning at an intersection. Given equivalent accelerating characteristics of STAA and non-STAA vehicles, the sight distance required to the left and the right to cross an intersection should be affected only by vehicle length. AASHTO require- ments, which are based on the WB-50 for trucks, call for a sight distance of 1,000 ft to cross a two-lane, 55-mph arterial from a stopped position (AASHTO 1984, 791). Hall estimates that a 48-ft tractor-semitrailer would require about 5 percent more sight distance, and a 65-ft long twin trailer truck could require up to 10 percent more (Hall 1986, 160). He concludes that these represent relatively minor changes to existing practice. Sight distance for turning is independent of vehicle length unless the intersection has very restrictive geometry, which could result in longer turning times for longer-wheelbase STAA tractor-semitrailers. The main factor here is vehicle acceleration, and it appears that STAA vehicles differ little from the WB-50 in this respect (Hall 1986, 161). A recent review of the assumptions underlying current AASHTO design policies for intersection sight distance (Mason et al. 1989) found that they may not be sufficiently sensitive to the characteristics and performance of STAA vehicles (i.e., length, acceleration and decelera-
Highway Design 147 tion characteristics). Adjustments to the current AASHTO intersection sight distance models, incorporating these factors, resulted in increased sight distance requirements, partiularly for turning at an intersection, for most large combination vehicles (Mason et al. 1989, 26).9 Thus intersec- tion sight distance requirements should be carefully considered for all roads with high volumes of combination vehicle traffic. Sight Distance at Railroad-Highway Grade Crossings Sight distance at railroad-highway grade crossings for large combination vehicles has obvious safety ramifications. Adequate sight distance is needed to stop the vehicle before it reaches the crossing area if a train is coming or to clear the tracks from a moving, or stopped, position if the truck has already moved into the crossing area. The key factors of concern for calculating sight distance for large trucks are vehicle length and acceleration and braking characteristics. A com- parison of AASHTO guidelines for sight distance requirements at rail- road-highway grade crossings based on the WB-60 (a 65-ft-long twin trailer truck) with sight distance requirements based on varying truck length and braking and acceleration characteristics indicated that assump- tions about braking performance were most critical in assessing the ade- quacy of sight distance requirements (personal communication with D. W. Harwood and W. D. Glauz, Midwest Research Institute, January 26, 1989). If braking distances were calculated assuming a "worst perfor- mance" truck driver (i.e., operating the truck at 62 percent of its braking efficiency), sight distance requirements were considerably greater than those of the AASHTO guidelines. This inadequacy, however, does not differ significantly for STAA and non-STAA vehicles, which suggests that state and local officials should give special consideration to the adequacy of sight distance at railroad-highway grade crossings on roads with any large combination vehicle traffic. Interchange and Ramp Design In many instances STAA vehicles will exit the National Network onto access roads via interchanges and ramps Thus interchange and ramp design for large trucks is another important consideration in determining the adequacy of roadway geometry for STAA vehicles. A summary article in a recent study of truck accidents on interchange
148 PROVIDING ACCESS FOR LARGE TRUCKS ramps (Ervin et al. 1986b) concluded that AASHTO geometric design policies for ramps make little or no allowance for the special stability and control requirements of trucks. The design vehicle was the WB-50, which suggests that even less allowance is made for the longer STAA vehicles. The ability of large trucks to negotiate ramps is affected by stability factors, such as the height of the truck relative to its width and loading arrangements, and by control factors, such as braking and high-speed offtracking. AASHTO design allowances for ramp curves, which are based on passenger cars, afford little margin of safety for large trucks with high centers of gravity and low rollover thresholds. Moreover, the actual roll stability limit for trucks is significantly less than the theoretical limit (Hall 1986, 163). Curbs, now discouraged by AASHTO, are present on the outside edge of many ramps and may contribute to rollover. At high speeds, the trailers of tractor-semitrailers and twins may swing out so that the rearmost axles trace a path that is outside the path traced by the tractor axles, an effect known as high-speed or negative offtracking (Ervin et al. 1986b, 87). Problems occur when the outer trailer tire approaches a curb at a sideslip angle, causing the tire to resist mounting the curb and tripping the vehicle. Finally, inadequate deceleration lanes before sharply curved ramps result in both truck rollovers and jackknifes. AASHTO guidelines for lengths of deceleration lanes are based on automobile deceleration levels of 0.24 g from 55 mph; large trucks decelerating from 55 to 25 mph may be limited to a steady deceleration of 0.16 g and thus require far longer deceleration lanes (Ervin 1986b, 85). The primary reason for this is the poorer braking performance of large trucks. There is considerable evi- dence to suggest that the actual braking efficiency of trucks is approx- imately 50 percent or less of theoretical braking capability (Ervin et al. 1986b, 84). STAA vehicles are unlikely to perform better on ramps and inter- changes than the vehicles they replace. High-speed offtracking, which may result in rollover on curbed ramps, increases with the number of trailing units and thus is more severe for STAA twin trailer trucks than for the tractor-semitrailers they replace. There is no evidence to suggest that the braking capability of STAA vehicles, and thus their ability to negoti- ate sharply curved ramps, is any better than that of the vehicles they replace. Because of the inadequacy of most ramp designs for all large trucks and because STAA vehicles are unlikely to perform better on these facilities than the vehicles they replace, special attention should be given to access routes that require STAA vehicles to use interchanges and ramps.
Highway Design 149 FINDINGS A review of the literature on the relationship between STAA vehicle operating characteristics and roadway geometric design identified the key features of concern (Table 6-4). Vehicle length is a more critical factor than vehicle width. The modest increment of 6 in. in width to 102-in. vehicles has already been taken into account in AASHTO's most current geometric design policies and was shown to have only a minor effect on such features as passing sight distance requirements and lateral separa- tion and placement of vehicles on two-lane roads. Incorporating the other dimensions of STAA vehicles into geometric design policies is not a trivial task because the dimensions specified by the 1982 act are not sufficient to describe these vehicles for purposes of design. Several key problems associated with STAA vehicle length, however, were identified. The first is the ability of STAA vehicles to negotiate sharp horizontal curves on narrow two-lane roads. The offtracking problems of the longer-wheelbase tractor-semitrailers make it difficult for truck drivers to negotiate the turns without encroaching into the oncoming traffic lane or running off the road. The sharper the curve and the narrower the traffic lanes and shoulders, the greater the offtracking; the potential for encroachment into the oncoming traffic lane can present a significant hazard. A related problem is that of sight distance for passing on two-lane roads. Automobiles passing an STAA vehicle or any other long combina- TABLE 6-4 PERFORMANCE PROBLEMS AND CHARACTERISTICS OF STAA VEHICLES BY GEOMETRIC FEATURE AND VEHICLE CONFIGURATION Geometric Feature STAA Tractor- Semitrailer STAA Twin Trailer Truck Passing sight distance - Vehicle length Horizontal curvature Offtracking - Rollover Rollover Lane and shoulder width Offtracking - Rollover Rollover Vehicle width Vehicle width Intersections Turns Offtracking - Sight distance Vehicle length Vehicle length Interchanges and ramps Rollover Rollover NoTE: Dash = less critical for this vehicle.
150 PROVIDING ACCESS FOR LARGE TRUCKS tion vehicle will spend significantly longer in the passing lane, particularly when passing an STAA twin trailer truck, than is provided by current practices for signing and marking no-passing zones. The additional time required to pass an STAA vehicle, however, is slight, and the require- ments for passing sight distance include a generous amount of time for the passing driver to abort the passing maneuver; this allowance will remain unchanged whether the vehicle passed is a passenger car or an STAA vehicle. STAA vehicle length may also affect the adequacy of sight distance at intersections and railroad-highway grade crossings. Recent reviews of AASHTO policies on both of these features suggest that current AASHTO guidelines may not accommodate most large combination vehicles. Thus special consideration should be given to the adequacy of sight distance at intersections and railroad-highway grade crossings on roads with any large combination vehicle traffic. Intersections with restrictive roadway geometry (i.e., short radii, nar- row lanes) also pose a problem for the longer-wheelbase STAA tractor- semitrailers but not for the STAA twin trailer trucks. The offtracking problems of the STAA tractor-semitrailers affect the ability of these vehicles to negotiate even intersections built to current AASHTO design standards. Right-hand turns at the intersection of two-lane roads, a configuration that is typical of many urban intersections, present the greatest difficulty because the roadway is likely to be too narrow to accommodate the turning truck without its encroaching onto the adjacent traffic lanes or riding up on the inside curb, or both. Because of the low speeds involved, the major consequence of this maneuver may be its effect on capacity and traffic flow, not on accident experience. Finally, the stability and control characteristics of STAA vehicles are likely to adversely affect their performance on many interchanges and ramps. When STAA vehicles enter or exit the National Network via an interchange or ramp, safety will be a major concern. The literature indicates that ramp design is often inadequate even for non-STAA trucks and that the likelihood of rollovers and jackknifes will be exacerbated for STAA vehicles. In sum, the geometric features that are of greatest concern for the operation of STAA vehicles are horizontal curves on narrow two-lane roads, turning radii at intersections with restrictive geometry, passing sight distance on two-lane roads, sight distance at intersections and rail- road-highway grade crossings, and the design of existing ramps and interchanges. The last three features are of concern not only for STAA vehicles but for all large combination vehicles.
Highway Design 151 IMPLICATIONS FOR DEVELOPING ACCESS POLICIES Roads with restrictive geometry can be an impediment to providing access for STAA vehicles. Studies of STAA vehicle handling and perfor- mance relative to specific roadway geometric features provide the follow- ing guidance: STAA vehicles differ in their ability to handle different geometric features. Thus a particular geometric feature may present difficulty for the STAA tractor-semitrailer but not for the STAA twin trailer truck. On balance, because of their offtracking problems, the longer-wheelbase STAA tractor-semitrailers have more problems than twins in many loca- tions with restrictive geometry. The impacts on safety of STAA vehicles traveling on roads with restrictive geometry will differ depending on the geometric feature in- volved. For example, the safety consequences of STAA tractor-semi- trailers negotiating intersections with restrictive geometry are likely to be less severe than those of operating on narrow two-lane roads with sharp curves. The magnitude of the hazard depends in part on the volume and composition (i.e., the number of STAA vehicles in the traffic stream) of traffic at critical locations. Mitigative measures may make it possible to avoid costly upgrading of some roads with restrictive geometry. Regulation of wheelbase dimen- sions, particularly the distance from the kingpin to the rear axle or axles, can reduce offtracking of STAA tractor-semitrailers on horizontal curves and at intersections. However, underride guards or better illumination of the rear of the trailer may be required on long tractor-semitrailer units to reduce any adverse impacts of increased trailer overhang from a short- ened trailer wheelbase. AASHTO guidelines for intersection sight distance, railroad-high- way grade crossings, and interchanges and ramps are inadequate for non- STAA as well as STAA vehicles. These features warrant special attention if they are present on roads with high volumes of combination vehicle traffic. NOTES 1. The new design vehicles and policies have been approved by AASHTO's Subcom- mittee on Design. Final approval by AASHTO's Executive Committee is expected this year, and the additions will appear in a revised policy guide.
152 PROVIDING ACCESS FOR LARGE TRUCKS Nine states have both identified needed improvements and modified their geomet- ric design practices: California, Idaho, Illinois, Michigan, Minnesota, Oregon, Utah, Washington, and Wisconsin. Alabama, Arizona, Georgia, Kentucky, New Mexico, and Vermont have only identified needed geometric improvements; Flor- ida, Iowa, Maine, Mississippi, Nebraska, Ohio, South Carolina, and South Dakota have only modified their geometric design standards. This calculation assumes that the overtaking vehicle is passing at a speed of 15 ft/sec and that the distance traversed by the opposing vehicle is equal to two-thirds of the distance traveled in the left lane by the passing vehicle (see Gericke and Walton 1981, 15). The initial maneuver distance is calculated from the following equation: 1.47 x t(V - m + a x t/2),wheret = initial maneuver time (seconds), V = average speed of passing vehicle (miles per hour), m = speed difference between the two vehicles (miles per hour), and a = average acceleration (miles per hour per second) (Gericke and Walton 1981, 16). The WB-50, assuming 300 lb/hp, requires 3,000 ft to accelerate from 40 to 50mph on a level roadway. The kingpin is a boltlike device on the underside of the front of a semitrailer that fits into the tractor's fifth wheel to couple the tractor and the trailer (Guide for Monitoring and Enhancing Safety on the National Truck Network 1986, 40). The computer tabulations were based on an offtracking model developed by the University of Michigan Transportation Research Institute and modified and ex- panded by the California Department of Transportation. The calculation assumes a tractor wheelbase length of 15 ft, a 1-ft offset from the tandem axle to the fifth wheel, and a 40-ft trailer length, measured from the kingpin to the centerline of the semitrailer's rear axle (Hall 1986, 162). The authors, however, questioned whether such increased sight distance require- ments were necessary for safe operation at intersections and suggested that, when any of the AASHTO guidelines are revised, the underlying assumptions on which the requirements are based be carefully examined (Mason et al. 1989, 26). REFERENCES ABBREVIATIONS AASHTO American Association of State Highway and Transportation Officials FHWA Federal Highway Administration NCHRP National Cooperative Highway Research Program TRB Transportation Research Board AASHTO. 1984. A Policy on Geometric Design of Highways and Streets. Wash- ington, D.C. DeCabooter, P. H., and C. E. Solberg. 1989. Operational Considerations Relat- ing to Long Trucks in Urban Areas. In Transportation Research Record. TRB, National Research Council, Washington, D.C., forthcoming. Ervin, R. D., R. L. Nisonger, C. C. MacAdam, and P. S. Fancher. 1986a. Influ- ence of Size and Weight Variables on the Stability and Control Properties of
Highway Design 153 Heavy Trucks. FHWAIRD-83/029. Transportation Research Institute, Ann Arbor, Mich.; FHWA, U.S. Department of Transportation, July, 199 pp. Ervin, R. D., C. C. MacAdam, and M. Barnes. 1986b. Influence of the Geomet- ric Design of Highway Ramps on the Stability and Control of Heavy-Duty Trucks. In Transportation Research Record 1052. TRB, National Research Council, Washington, D.C., pp. 77-89. Fancher; P. S. 1986. Sight Distance Problems Related to Large Trucks. In Trans- portation Research Record 1052. TRB, National Research Council, Washing- ton, D.C., pp. 29-35. Gericke, 0. F., and C. M. Walton. 1981. Effect of Increased Truck Size and Weight on Rural Highway Geometric Design (and Redesign) Principles and Practices. In Transportation Research Record 806. TRB, National Research Council, Washington, D.C., pp 13-21. Gillespie, T. D. 1986. Methods for Predicting Truck Speed Loss on Grades. FHWAIRD-86/059. University of Michigan Transportation Research Institute, Ann Arbor; FHWA, U.S. Department of Transportation, Oct., 170 pp. Guide for Monitoring and Enhancing Safety on the National Truck Network. 1986. FHWA, U.S. Department of Transportation, Oct., 58 pp. Hall, J. W. 1986. The Influence of Large Trucks on Geometric Design. Proc., 23rd Paving and Transportation Conference, University of New Mexico, Albu- querque, Jan., pp. 155-169. Harwood, D. W., and J. C. Glennon. 1989. Passing Sight Distance Design for Passenger Cars and Trucks. In Transportation Research Record. TRB, National Research Council, Washington, D.C., forthcoming. Hirsch, T. J. 1986. Longitudinal Barriers for Buses and Trucks. In Transportation Research Record 1052. TRB, National Research Council, Washington, D.C., pp. 95-102. Hummer, J. E., C. V. Zegeer, and F. R. Hanscom. 1988. Effects of Turns by Larger Trucks at Urban Intersections. In Transportation Research Record. TRB, National Research Council, Washington, D.C., forthcoming. Mason, J. M., Jr., K. Fitzpatrick, and D. W. Harwood. 1989. Intersection Sight Distance Requirements for Large Trucks. In Transportation Research Record. TRB, National Research Council, Washington, D.C., forthcoming. Safwat, K. N. A., and C. M. Walton. 1986. Expected Performance of Longer Combination Vehicles on Highway Grades. In Transportation Research Record 1052. TRB, National Research Council, Washington, D.C., pp. 63-77. Seguin, E. L., K. W. Crowley, P. C. Harrison, Jr., and K. Perchonok. 1982. The Effects of Truck Size on Driver Behavior. FHWA/RD-81/170. FHWA, U.S. Department of Transportation, March, 138 pp. TRB. 1986. Twin Trailer Trucks. Special Report 211. National Research Council, Washington, D.C., 388 pp. Troutbeck, R. 1984. The Effect of Trucks on Australian Two-Lane Highway Traffic. ITE Journal, Vol. 54, No. 3, March, pp. 14-17. Whiteside, R. E., T. Y. Chu, J. C. Cosby, R. L. Whitaker, and R. Winfrey. 1973. Changes in Legal Vehicle Weights and Dimensions: Some Economic Effects on Highways. NCHRP Report 141. TRB, National Research Council, Washington, D.C., 189 pp. Winkler, C. B., P. S. Fancher, 0. Carsten, A. Mathew, and P. Dill. 1987. Improving the Dynamic Performance of Multitrailer Vehicles: A Study of Inno- vative Dollies, Vol. 1: Technical Report. FHWAIRD-86/161. FHWA, U.S. Department of Transportation, Dec., 246 pp.
7 Traffic Operations and Safety T RAFFIC CONGESTION HAS BECOME a major transporta-tion concern, particularly in the nation's metropolitan areas. Highway engineers must address not only the adequacy of high- way geometry to accommodate STAA vehicle travel off the National Network but also the effects of these longer and wider vehicles on traffic operations. Highways and intersections are built to accommodate a maxi- mum flow of traffic, generally expressed as a number of vehicles per hour. As this capacity flow is approached, traffic congestion and delays in- crease, significantly degrading the efficiency with which traffic can be moved and the quality of traffic flow. Highways are designed to handle a mix of vehicle types, but not all vehicles have the same effect on traffic flow. The introduction of large trucks, in particular, adversely affects highway capacity because of their size relative to that of other vehicles and their poorer operating perfor- mance, specifically their capability to accelerate, decelerate, and main- tain speed on grades (TRB 1985, 1-11). The impact of these characteris- tics is most pronounced on two-lane highways with grades, where the presence of large, slow trucks creates bottlenecks that reduce traffic flow, and at intersections, where large trucks increase clearance times and thus cause queuing and delays. Both of these situations are present on many roads open to STAA vehicles. The purpose of this chapter is to assess the impact of the introduction of STAA vehicles relative to that of the vehicles they replace on traffic operations. The chapter begins with a discussion of how highway capacity is measured and of the impact of heavy trucks on capacity; then the technical literature is reviewed to determine what is known about the factors affecting STAA vehicle impact on traffic operations under various traffic and highway conditions; finally, a summary assessment is provided 155
156 PROVIDING ACCESS FOR LARGE TRUCKS of the net impact of the introduction of STAA vehicles on traffic opera- tions. MEASURING THE IMPACT OF HEAVY TRUCKS ON HIGHWAY CAPACITY To simplify the design of highways and intersections, traffic engineers express the traffic volume created by a traffic stream of different types of vehicles in terms of passenger-car equivalents (PCEs). First introduced in the 1965 Highway Capacity Manual, the standard guide for determining highway design capacity, the concept of PCE is defined in the revised 1985 manual as "the number of passenger cars that would consume the same percentage of . . . [a roadway's] . . . capacity as one truck, bus, or recre- ational vehicle under prevailing roadway and traffic conditions" (TRB 1985, 3-11). PCEs for trucks vary as a function of grade, road type, traffic volume (total and truck traffic), and traffic distribution. Table 7-1 gives PCEs for trucks for two of these key factorsâroad grade and type of highwayâthat range from 1.7 on level multilane freeways to 12.0 on mountainous two- lane highways. Data in the table indicate that, when trucks are present in the traffic stream, the type of terrain, particularly long, steep upgrades, has a more adverse effect on highway capacity than does the type of highway. This finding reflects the difficulty that heavy vehicles have maintaining speed on upgrades. However, for a given type of terrain, the effects of truck operation are more severe on two-lane than on multilane highways. An illustration shows how PCEs can be used to estimate capacity loss due to trucks operating under various conditions. Assume, for example, a two-lane road on which all of the traffic is passenger cars and the maxi- mum design flow of cars in each direction per hour under ideal conditions is 2,800 (TRB 1985, 8-8).' If trucks are introduced and represent 10 percent of the traffic stream, still assuming ideal conditions (i.e., PCE = TABLE 7-1 PASSENGER CAR EQUIVALENTS FOR TRUCKS BY TYPE OF HIGHWAY AND TERRAIN (TRB 1985, 8-9, 3-13) Type of Type of Terrain Highway Level Rolling Mountainous Multilane freeway 1.7 4.0 8.0 Two-lane highway 2.0-2.2 4.0-5.0 7.0-12.0
Traffic Operations 157 2), highway capacity is reduced by 9 percent to 2,545 vehicles per hour.2 If the same volume of truck traffic is introduced, but under the worst conditions (i.e., PCE = 12), highway capacity is more than halved to 1,330 vehicles per hour. PCEs provide a broad gauge of the effect of truck traffic on highway capacity for a range of operating and highway conditions. However, they do not provide a means of differentiating impacts by truck type. The PCEs for trucks in the Highway Capacity Manual are based on an average of medium and heavy trucks combined. Although other researchers have attempted to distinguish among truck types, lack of agreement on a common definition of PCE makes it difficult to use these results (Krammes and Crowley 1986, 10). Thus, instead of directly measuring the incremental effects on highway capacity of introducing STAA vehicles in the traffic stream, an attempt is made here to infer these effects by examining the vehicle factors that are most likely to affect traffic opera- tions and determining to what extent these factors have been affected by the changes in vehicle size and weight authorized by the 1982 STAA. FACTORS AFFECTING STAA VEHICLE IMPACT ON TRAFFIC OPERATIONS A review of the literature on the impact of large trucks on traffic opera- tions (Larson and Hanscom 1984) identified two specific characteristics of STAA vehicles that are likely to adversely affect highway capacity: (a) higher average vehicle weight, which reduces vehicle speed and accelera- tion capabilities, and (b) added vehicle length, which increases passing time and distance and generally reduces highway capacity; these effects, however, may be mitigated by smaller increases in truck traffic, attribut- able to the use of the larger STAA vehicles, than would otherwise have been experienced with equipment of pre-STAA dimensions. Vehicle Weight To the extent that carriers have adopted the larger, and on average heavier, STAA equipment without increasing tractor horsepower, vehicle weight-to-power ratios are raised, affecting operating performance. The largest operational impact of higher weight-to-power ratios is reduced truck speed and increased speed differentials between trucks and other traffic (Larson and Hanscom 1984, 55). These effects not only degrade
158 PROVIDING ACCESS FOR LARGE TRUCKS traffic flow, they also increase accident risk. Several studies have docu- mented that wide variations in vehicle speeds increase the probability of accidents (Solomon 1964, Cirillo 1968, and Hauer 1971). Traffic Impacts on Grades The effects of higher weight-to-power ratios are most pronounced on two- lane upgrades where slow-moving trucks may cause formation of platoons of following vehicles and passing restrictions may exacerbate delays (TRB 1985, 8-8) . The literature on truck performance on highway grades was reviewed to determine what is known about the performance of STAA vehicles relative to the vehicles they replace. TRB's Twin Trailer Trucks identified a few studies that documented a speed differential between twin trailer trucks and tractor-semitrailers on grades (TRB 1986, 285). The poorer speed performance of twin trailer trucks was attributed to their slightly greater weight and poorer aerody- namic properties; they encounter more air resistance than do tractor- semitrailers because of their greater overall length and the presence of the second gap between the trailers (TRB 1986, 286). (The aerodynamic differences are insignificant, however, at slow speeds on grades.) More recent information gathered by the Midwest Research Institute on the impact of truck characteristics on highway geometric design and traffic operations corroborated these findings; the final climbing speed of twin trailer trucks on grades of varying severity was from 4 to 7mph slower than that of tractor-semitrailers for the median performance vehicle (D. W. Harwood and W. D. Glauz, personal communication, January 25, 1989). No studies could be found on the speed differential on grades between the longer STAA tractor-semitrailers and the shorter vehicles they replace. Recent information on truck weight-to-power ratios for a range of gross vehicle weights up to 80,000 lb (Figure 7-1) shows a decline in truck weight-to-power ratios over the last several decades as a result of increases in engine horsepower (Gillespie 1986, 76-78). Assuming that the long- range trend is for continued improvement, that is reduction, in the weight-to-horsepower ratio of trucks, the slightly greater weight of STAA vehicles relative to the vehicles they replace should not cause a substantial degradation in traffic flow. Comparison of the performance of twin trailer trucks and tractor- semitrailers with that of the design vehicle (i.e., a truck with a weight-to- power ratio of 300 lb/hp), on which AASHTO bases its design guidelines for highway grades (AASI-ITO 1984, 259-278), indicates that perfor-
I- I. 0 E .0 Traffic Operations 159 -- 1949 Study 1955 Study ---- 1963 Study 1973 Study 1977 Study University of Michigan Transportation a Research Institute 1985 EMEMNE MMEMNAPPEN MENSHEME [NOMMMMME 10 20 30 40 50 60 70 80 GROSS WEIGHT, thousands of pounds (1000 lb = 0.454 Mg) FIGURE 7-1 Trends in weight-to-power ratios of trucks, 1949 to 1985 (Gillespie 1986, 77 and Olson et al. 1984, 152). mance of twin trailer trucks is similar to, and that of tractor-semitrailers better than, the AASHTO design vehicle.4 To the extent that grades meet or exceed AASHTO design guidelines, they should accommodate STAA vehicles. Roads on the National Network generally meet these guidelines; access roads, especially in mountainous areas, however, are less likely to do so. Traffic Impacts at Intersections The larger and heavier STAA equipment may also affect truck accelera- tion capabilities at signalized intersections and thus increase clearance times. Molina et al. addressed the impact of large trucks at intersections in a recent study. The objective was to develop PCEs for various types of .600 500 400 300 20C ICC 0 0
160 PROVIDING ACCESS FOR LARGE TRUCKS trucks traveling straight through a level, signalized intersection based on vehicle acceleration rates and position in the queue (Molina et al. 1987, 2). The analytical model developed to estimate PCEs for various truck types was based on a comparison of the total travel time required for a queue with one truck in it to clear a signalized intersection5 with the time required for a queue made up exclusively of passenger cars. The position of the truck in the queue was varied (Molina et al. 1987, 27). The results were averaged for two types of trucks: a light truck, typical of a small delivery truck, and a heavy truck, representing a combination vehicle with five or more axles. PCEs for these truck types were 1.7 and 3.7, respectively (Molina et al. 1987, 36). As shown in Figure 7-2, both were higher than the 1.5 PCE truck factor recommended in the 1985 Highway Capacity Manual for calculating signalized intersection capacity, which suggests that the manual overstates capacity at intersections with heavy truck traffic (Molina et al. 1987, 7). The results also showed that, for heavy trucks, the truck's position in the queue has a pronounced effect on 900 800 a. 700 0 600 500 400 0 5 10 15 20 25 PERCENTAGE TRUCKS FIGURE 7-2 Comparison of capacity reduction at signalized intersections by truck type and volume of truck traffic (Molina et al. 1987, 37); S = saturation flow, pcphgpl = passenger car per hour of green time per lane, g = minimum green time in seconds, C=cycle length in seconds, vphpl=volume per hour per lane, HCM = Highway Capacity Manual.
Traffic Operations 161 PCE; the further back the truck is in the queue, the longer the time it has to accelerate and the lower its PCE (Molina et al. 1987, 41). Although the Molina study differentiates among broad categories of trucks, it does not provide sufficient information to distinguish between the performance of STAA and non-STAA vehicles at intersections. The closest approximation can be found in a study conducted by Olson et al. that compared the acceleration capabilities of several heavy combination vehicles with that of the WB-50, the 37-ft semitrailer that AASHTO uses as its design vehicle for intersections with heavy truck traffic (see Chapter 6). The study found that the average acceleration level of "typical" heavy trucks6 was better than that assumed for the WB-50 (Olson et al., 1984, 157-158). Again, these results reflect AASHTO's conservative assump- tions about truck weight-to-power ratios. Summary The increased size and average weight of STAA vehicles relative to the equipment they replace may increase vehicle weight-to-power ratios in the short term, resulting in some degradation in vehicle performance. A few studies have documented that twin trailer trucks perform more poorly on grades than do tractor-semitrailers because of the twins' greater size and poorer aerodynamic characteristics. However, recent data on trends in weight-to-power ratios of large trucks indicate a general decline in these ratios because of improvements in engine technology. Continued improvements should reduce the negative impacts of the slightly heavier STAA vehicles on traffic flow. STAA vehicle performance exceeds that of the design vehicle on which AASHTO guidelines for design of highway grades and intersections are based, primarily because of AASHTO's conservative estimates of truck weight-to-power ratios. Highways that meet or exceed current AASHTO guidelines should accommodate STAA vehicles, but many access roads are not designed to these standards. Vehicle Size Vehicle size is the second vehicle characteristic that affects traffic opera- tions. Larger trucks literally occupy more space on the road than most other vehicles, reducing traffic flow and limiting passing maneuvers. Although the increased width of STAA vehicles can adversely affect traffic flow on narrow roads, added vehicle length has a more critical
162 PROVIDING ACCESS FOR LARGE TRUCKS impact, affecting passing behavior on two-lane roads and reducing traffic capacity and causing delays at intersections. Two-Lane Roads Large trucks have a more adverse impact on traffic flow on two-lane roads than on multilane highways because of their effect on passing behavior. This impact is exacerbated by poor roadway geometry, such as narrow lanes and curves that restrict passing zones, and by the volume of traffic; as traffic volume rises, passing demand increases rapidly and passing opportunities decline sharply (Messer 1983, 3). Traffic volumes tend to be low on many two-lane roads, particularly in rural areas, although sight distance for passing is restricted on many such roads. Nearly two-thirds of rural arterial mileage, the majority of which is two-lane roads,7 has average traffic volumes that are less than 20 percent of the maximum traffic flow that can reasonably be expected to negotiate these roadway sections (Table 7-2). Urban arterials, fewer of which are two-lane roads, tend to be more congested: less than one-quarter of the mileage experiences a service volume flow ratio of 0 to 0.21, and more than half has a ratio greater than 0.40 (Table 7-2). A few studies have examined the impacts of trucks of different lengths and widths on two-lane highways. Troutbeck investigated the effect of vehicle length on passing behavior on rural two-lane roads.8 He found that passing time and distance are increased by 5 percent for a passenger vehicle (a 16-ft station wagon) passing a 65- versus a 52-ft truck (Trout- beck 1982, 325-326) assuming equivalent vehicle speeds. However, if the truck is traveling more slowly than the passenger vehicle, which is often the case on roads with restrictive geometry, passing time is reduced. Troutbeck calculated that the 85th percentile passing time around a 16-ft passenger car is the same as the passing time around a 52-ft truck traveling TABLE 7-2 PERCENTAGE OF ARTERIAL MILEAGE CLASSIFIED BY VOLUME-TO-SERVICE FLOW RATIO (Highway Statistics 1987 1988, 158, 160-161) Type of Volume-to-Service Flow Ratio Arterial <0.21 0.21-0.40 0.41-0.70 >0.71 Rural 62.8 26.4 8.6 2.2 Urban 22.6 24.8 25.2 27.4
Traffic Operations 163 6 mph slower or around a 65-ft truck traveling 8 mph slower (Troutbeck 1982, 326). He also found that between 70 and 90 percent of the time required for passing maneuvers around both cars and trucks is spent pulling out and returning to the traffic lane (Troutbeck 1982, 326). Although cars spend more time in the initial phase of the passing maneuver when overtaking a truck, because they tend to follow the truck at a greater distance, this additional time is offset at the end of the passing maneuver by the tendency of passenger cars to "cut in" on trucks more than on cars. Thus times for the combined initial and final phases of the passing maneuver are similar; although the time alongside the overtaken vehicle increases when the latter is a truck, this represents only a small share of thetotal passing time. Zegeer et al. analyzed the behavior of oncoming drivers. on two-lane rural roads as they approached trucks of various lengths, ranging from the smaller 40- to 45-ft tractor-semitrailers to the 48-ft tractor-semitrailers and the twin 28-ft trailer trucks. The longer STAA vehicles caused drivers to slow more and to move closer to, or stray over, the pavement edge than did the shorter vehicles. The differences were statistically significant but not numerically large, which led the .authors to conclude that other factors, such as the skill of the driver in positioning the truck in the lane and the geometric characteristics of the roadway itself, had a greater effect on the oncoming traffic flow than did the type of truck (Zegeer et al. 1987, 90). Seguin et al. examined the effect of vehicle width on passing behavior on rural two-lane roads. They found that, as truck width was increased from 96 to 102 in. up to 114 in., passing became more difficult. Increased truck width reduced lateral distances between passers (overtaking and oncoming) and the truck; forced oncoming vehicles closer to the roadway edge; and, as Troutbeck found, increased spacing between vehicles in prepass maneuvers, suggesting reduced ability to see around wider trucks and an intimidation effect (Seguin et al. 1982, 8-9).. Although these factors degrade the quality of traffic flow, the study results suggest that their effect is minor for width increases up to 102 in. For example, the headway difference of 7 ft for vehicles following 96-in, versus 102-in. trucks proved statistically insignificant (Seguin et al. 1982, 55). Intersections Truck size may also affect traffic capacity and flow at intersections. The effect of vehicle size on intersection capacity, particularly the turning
164 PROVIDING ACCESS FOR LARGE TRUCKS problems of the longer-wheelbase tractor-semitrailers discussed in Chap- ter 6, is examined. Zegeer et al. examined the impact of right- and left-turning trucks of STAA and pre-STAA dimensions at urban intersections. Among the traffic-related factors they studied were the clearance time of the truck through the intersection and traffic conflict events, such as weaving, stopping, and backing by vehicles in the traffic stream and by the truck (Zegeer et al. 1987, 21). Field tests showed significant differences in turning time for different types of trucks. STAA twin trailer trucks had a statistically significant longer turning time (1.5 to 2.5 sec more) than 40- or 45-ft tractor- semitrailers at intersections with minimal geometric restrictions because of the twins' greater length; however, no statistically significant difference in turning times was found at intersections with more restrictive geome- try,9 suggesting that the maneuverability of twin trailer trucks on turns may partly offset the negative effects of their greater length under these conditions (Zegeer et al. 1987, 88). The operational problems caused by 48-ft tractor-semitrailers with their rear axles in the farthest back position were significantly greater than when the axles were brought forward, reflecting the problems caused by offtracking of the longer-wheelbase tractor-semitrailer (see Chapter 6). 10 For example, right-turn times aver- aged 11.3 sec with the axles back compared with 7.3 sec with the axles forward (Zegeer et al. 1987, 89). No significant differences were found in vehicle conflict rates by truck type (Zegeer et al. 1987, 88). There are more opportunities to manage traffic flow and reduce ad- verse effects on capacity short of major reconstruction at signalized intersections than at other highway locations (TRB 1985, 9-3). Studies of the performance of long-wheelbase tractor-semitrailers at selected two- lane signalized urban intersections in Wisconsin indicated that, even at relatively high traffic volumes, trucks found sufficient gaps in the cross street traffic stream under certain traffic signal conditions to negotiate the more demanding right turn with only moderate queuing (DeCabooter and Solberg 1988, 12). Observed acceptable gap sizes ranged from 10 sec for a "roll-through" right turn for the truck approach and no stops on the cross street into which the truck was turning to 23 sec for a four-way stop (DeCabooter and Solberg 1988, 15-17). These researchers conclude that, within certain physical constraints (i.e., minimum curb-to-curb street widths), the decrease in traffic capac- ity at intersections where long trucks are part of the traffic stream can be reduced by changes in signalization. Traffic flow is maximized at sig- nalized intersections with no-stop right turns on the truck approach road (although this requires acceleration lanes and large turn radii) and no
Traffic Operations 165 signal on the cross street. This treatment allows truck drivers to take advantage of gaps as they occur. If traffic on the cross street is stopped, the signal should be set far enough back from the intersection to provide space for truck drivers to negotiate the turn (DeCabooter and Solberg 1988, 28). The survey of state highway and transportation departments conducted for this study found that no state has yet modified its traffic control operations to facilitate movement of STAA vehicles on access roads. Summary The added length and width of STAA vehicles increase the difficulty of passing on two-lane roads, particularly as traffic volume rises, and may cause delays at intersections, particularly as trucks make turning maneu- vers. Passing time and distance are increased by the greater length of STAA tractor-semitrailers and twin trailer trucks, but the increase in passing time around an STAA vehicle compared with shorter trucks of pre-STAA dimensions is modest. Traffic volume on many two-lane roads, particularly in rural areas, tends to be low, although sight distance for passing will be restricted on many such roads. Added vehicle width also increases the difficulty of passing by restricting sight distance and increas- ing vehicle prepass headways and by reducing lateraldistances between passing vehicles and the truck; however, these effects were found to be minor for the small increase in vehicle width from 96 to 102 in. At intersections the effect of greater STAA vehicle size is most evident in turning maneuvers. Twin trailer trucks take longer to turn than the pre- STAA 45-ft tractor-semitrailers at intersections with minimal geometric problems because of the former's greater length. Differences in turning times are the same, however, at intersections with restrictive geometry because of the turning maneuverability of the twins. The longer-wheel- base tractor-semitrailers with their rear tandem axles set back take signifi- cantly longer to negotiate turns than do the same vehicles with their rear tandem axles moved forward to create a configuration similar to that of the shorter-wheelbase vehicles they replace. Signalization provides op- portunities, short of major reconstruction, to mitigate the adverse im- pacts of STAA vehicles on traffic flow and capacity at intersections. These opportunities are not present at other locations and may be limited by the physical characteristics (i.e., minimum pavement width on approach roads) of intersections (see Chapter 6). The turning ability of the trucks themselves may be improved by regulating tractor-trailer wheelbase length at inadequately designed intersections as discussed in Chapter 6.
166 PROvIDING ACCESS FOR LARGE TRUCKS Other Vehicle-Related Factors Affecting 'J}affic Operations The TRB study committee for Twin Trailer Trucks conducted a literature review (TRB 1986, Appendix E) that examined the effects of STAA vehicles on several other important factors that affect traffic flow. The highlights of that review are summarized here. In wet weather, large trucks generate spray and splash water, snow, or slush on passing and following vehicles, reducing driver vision (TRB 1986, 291). The longer STAA tractor-semitrailers are likely to aggravate these phenomena slightly because their added weight will displace more water and their added length will expose passing motorists for longer periods to both splash and spray (TRB 1986, 292). Limited tests suggest that driver visibility is less severely impaired by twin trailer trucks, in part because their single axles generate less spray than do the tandem axles of tractor- semitrailers (TRB 1986, 291-292). The aerodynamic forces acting on a vehicle are changed when a vehicle passes a large truck in an adjacent lane; lateral displacement of the smaller vehicle may result without steering adjustments. The increased length and width of STAA vehicles as well as the gap between the two twin trailers are likely to increase aerodynamic buffeting, but the review concluded that the effects are negligible (TRB 1986, 293). Finally, large trucks may block the view of motorists. The effect of STAA vehicle width on passing sight distance has already been discussed. Another effect of the larger STAA vehicles is to block signs and signals that provide necessary information for safe traffic operation. The review found no studies that have examined the extent to which these effects have been aggravated by the introduction of STAA vehicles (TRB 1986, 293-294), but a more recent article suggests that the longer STAA vehi- cles do block signs from the view of drivers of passing and following vehicles (Schorr 1986, 104-105). In sum, the review and subsequent studies of other factors affecting traffic flow suggest that the quality of traffic flow is likely to be slightly degraded by the introduction of the longer and wider STAA vehicles relative to the vehicles they replace (TRB 1986, 177). Volume of Truck Traffic The magnitude of the adverse impacts of STAA vehicles on traffic capac- ity and flow depends on the volume of STAA traffic. As discussed in Chapter 2, the introduction of larger STAA vehicles led to a smaller increase in truck traffic than would have been experienced with equip-
Traffic Operations 167 ment of pre-STAA dimensions and thereby mitigated some of the adverse impact of truck travel on traffic operations. Although there will be degra- dations in traffic flow on roads with high traffic volumes and restrictive geometry, the net adverse affect on traffic operations of the slightly heavier, longer, and wider STAA vehicles is likely to be small. SUMMARY Traffic congestion has become a major transportation concern. Because of their size and poorer operating performance relative to passenger vehicles, large trucks adversely affect highway capacity and traffic flow. Two characteristics of STAA vehicles are likely to adversely affect highway capacity and traffic flow: (a) higher average vehicle weight and (b) added vehicle length. The greater size and average weight of STAA vehicles may increase vehicle weight-to-power ratios in the short term, reducing STAA vehicle speed and acceleration capabilities relative to those of trucks of pre-STAA dimensions. Poorer performance capabilities are most evident on two-lane upgrades, particularly for the longer and aerodynamically inferior twin trailer trucks, and at intersections. Recent data, however, suggest a continuing decline in truck weight-to-power ratios because of improvements in engine technology, which should miti- gate these performance decrements in the long run. STAA vehicle perfor- mance exceeds that of the design vehicles on which AASHTO bases its guidelines for design of highway grades and intersections. Highways that meet or exceed current AASHTO guidelines should be able to accommo- date STAA vehicles, but many access roads are not designed to these standards. The greater size of STAA vehicles increases the difficulty of passing on two-lane roads and causes delays at intersections, particularly as trucks make turning maneuvers. The time and distance required to pass the longer STAA vehicles are greater, but the increases relative to vehicles of pre-STAA dimensions are modest and may not create problems on two- lane rural roads where traffic volumes are low and passing sight distance is adequate. STAA vehicle turning maneuvers at intersections can slow clearance times and create delays, but opportunities exist to reduce these adverse impacts by changing signalization and by shortening the trailer wheelbase of the longer STAA tractor-semitrailers. Other factors that affect the quality of traffic flow, such as splash and spray, aerodynamic buffeting, and blocking the vision of motorists in smaller vehicles, will be slightly aggravated by the introduction of STAA vehicles.
168 PROVIDING ACCESS FOR LARGE TRUCKS The magnitude of these adverse impacts depends on the volume of STAA traffic. Because the introduction of the larger STAA vehicles has resulted in a smaller increase in truck traffic than would have been experienced with equipment of pre-STAA dimensions, the net adverse impact on traffic operations of the slightly heavier and larger STAA vehicles is likely to be small. NOTES The analysis assumes level terrain, 50-50 directional distribution of traffic, and 12- ft lanes (TRB 1985, 8-8). These calculations are based on the following equation from the 1985 Highway Capacity Manual: Total service flow rate = 2,800 x 1/[1 + PT (E - 1)] where PT = the proportion of trucks in the traffic stream, expressed as a decimal, and E = passenger-car equivalent for trucks (TRB 1985, 8-8). These effects are also present on long, steep downgrades where the slowing of heavy trucks to counter the momentum gained from their weight increases the speed differential between these trucks and passenger vehicles and causes speed reductions and delays for following vehicles (Hanscom 1981, 96). These comparisons are based on final climbing speeds of the 12.5 percentile vehicles (Gillespie 1986, 104). Total travel time for each vehicle was measured from the start of the green cycle to the time the vehicle's rear axle crossed the stop line (Molina et al. 1987, vi). The acceleration curves are based on tests of a 273-lb/hp truck, a 300-lb/hp design vehicle starting in first gear and starting in second gear, and an average accelera- tion level of 2 ft/sec2 approximating a typical truck with a weight-to-horsepower ratio of 300 lb/hp operating in 1969 (Olson et al. 1984, 157). Seventy-four percent of rural principal arterials other than Interstate highways are two-lane roads, and 95 percent of rural minor arterials are two lane. Forty percent of urban principal arterials other than Interstates and expressways are two-lane roads, and three-fourths of urban minor arterials are two lane (Highway Statistics 1987 1988, 146-149). 'T'pical lane widths were 12 ft, and shoulder widths were between 8 and 10 ft (Troutbeck 1982,. 318). None of the intersections had highly restrictive geometry; all legs of each intersec- tion had at least three lanes (Zegeer et al. 1987, 88). The study did not indicated how far the rear axles were brought forward. The right turn is considered the more critical maneuver because, with the inward offtracking of the rear trailer at low speeds, the truck has a greater probability of "cutting" the curb or of conflict with oncoming vehicles. REFERENCES ABBREVIATIONS AASHTO American Association of State Highway and Transportation Officials
Traffic Operations 169 FHWA Federal Highway Administration NCHRP National Cooperative Highway Research Program TRB Transportation Research Board AASHTO. 1984. A Policy on Geometric Design of Highways and Streets. Wash- ington, D.C. Cirillo, J. A. 1968. Interstate System Accident Research: Study II, Interim Report II. Public Roads, Vol. 35, No. 3. DeCabooter, P. H., and C. Solberg. 1988. Operational Considerations Relating to Long Trucks in Urban Areas. In Transportation Research Record. TRB, National Research Council, Washington, D.C., forthcoming. Gillespie, T. D. 1986. Methods for Predicting Truck Speed Loss on Grades. FHWAIRD-861059. University of Michigan Transportation Research Institute, Ann Arbor; FHWA, U.S. Department of Transportation, Oct., 170 pp. Hanscom, F. R. 1981. The Effect of Truck Size and Weight on Accident Experi- ence and Traffic Operations, Vol. 2: Traffic Operations. FHWAJRD-80/136. BioTechnology, Inc., Falls Church, Va; FHWA, U.S. Department of Transpor- tation, July, 22 pp. Hauer, E. 1971. Accidents, Overtaking and Speed Control. Accident Analysis and Prevention, Vol. 3, pp. 1-13. Highways Statistics 1987. 1988. FHWA. U.S. Department of Transportation. Krammes, R. A., and K. W Crowley. 1986. Passenger-Car Equivalents for Trucks on Level Freeway Segments. In Transportation Research Record 1091. TRB, National Research Council, Washington, D.C., pp. 10-17. Larson, E. E., and F. R. Hanscom. 1984. Traffic Operational Impact of Large Trucks: A Literature Review. Transportation Research Corporation, Hay- market, Va., Oct. 5. Messer, C. J. 1983. Two-Lane, Two-Way Rural Highway Level of Service and Capacity Procedures. NCHRP Project 3-28A. TRB, National Research Coun- cil, Washington, D.C., Feb., 51 pp. Molina, C. J., C. J. Messer, and D. B. Fambro. 1987. Passenger Car Equivalen- cies for Large Trucks at Signalized Intersections. FHWAfFX-87/397-2. Texas Transportation Institute, College Station; FHWA, U.S. Department of Trans- portation, May, 63 pp. Olson, P. L., D. E. Cleveland, P. S. Fancher, L. P. Kostyniuk, and L. W. Schneider. 1984. Parameters Affecting Stopping Sight Distance. NCHRP Re- port 270. TRB, National Research Council, Washington, D.C., June, 169 pp. Schorr, D. J. 1986. Traffic Control Device Problems Associated with Large Trucks. In Transportation Research Record 1052. TRB, National Research Council, Washington, D.C., pp. 102-106. Seguin, E. L., K. W. Crowley, P. C. Harrison, Jr., and K. Perchonok. 1982. The Effects of Truck Size on Driver Behavior. FHWAJRD-81/170. The Institute for Research, State College, Pa.; FHWA, U.S. Department of Transportation, March, 138 pp. Solomon,D. 1964. Accidents on Main Rural Highways Related to Speed, Driver, and Vehicle. FHWA, U.S. Department of Transportation. TRB. 1985. Highway Capacity Manual. Special Report 209. National Research Council, Washington, D.C., 516 pp. TRB. 1986. Twin Trailer Trucks. Special Report 211. National Research Council, Washington, D.C., 388 pp.
170 PROVIDING ACCESS FOR LARGE TRUCKS Troutbeck, R. J. 1982. Effect of Overtaken Vehicle Speed and Length on Over- taking Behavior on Two-Lane Rural Roads. Traffic Engineering and Control, Vol. 23, June, pp. 318-328. Zegeer, C.V., J.E. Hummer, and F. Hanscom. 1987. The Operation of Larger Trucks on Roads with Restrictive Geometry, Vol. 1: Final Report. FHWAJ RD-86/157. Goodell-Grivas, Inc., Southfield, Mich.; FHWA, U.S. Depart- ment of Transportation, Aug., 105 pp.
8 Highway Condition S TATE AND LOCAL HIGHWAY OFFICIALS are concerned that more widespread travel by STAA vehicles could accelerate the deterioration of transportation facilities, increase the cost of rehabilitation, and require more expensive new construction. Facilities of specific concern are pavements, bridges and culverts, and shoulders and highway appurtenances such as curbs, signs, and guardrails. The longer and wider combination vehicles authorized by the 1982 STAA increase vehicle payload capacity and thus the potential for higher average vehicle weights and axle loads. Expanded travel by these heavier vehicles, particularly on pavements and bridges built to lower design standards than the Interstate highway system, may accelerate the deterio- ration of these facilities. The operating characteristics of STAA vehicles, particularly the offtracking of the longer-wheelbase tractor-semitrailers, may also increase the frequency of vehicle encroachment onto shoulders, which can damage shoulder surfaces and roadside appurtenances. The purposes of this chapter are to Define more precisely the impacts of STAA vehicle travel on the service life of highway surfaces, bridges, and highway appurtenances typical of access roads; Assess the probable magnitude of any additional damage to these facilities caused by STAA vehicles relative to the vehicles they replace; and Determine the incremental costs that result from the added deterio- ration. The analysis draws heavily on existing techniques, such as the Ameri- can Association of State Highway and Transportation Officials' 171
172 PROVIDING ACCESS FOR LARGE TRUCKS (AASHTO's) method of analyzing pavement deterioration, and relevant research studies to determine what is known about the effect of these vehicles on the condition of highways, bridges, and highway appurte- nances. Interviews with carriers and shippers provided information on the probable use and travel patterns of different types of STAA vehicles. Examples are provided to illustrate the effects that allowing STAA vehi- cles to travel on typical access highways from which they have been barred would have on both incremental damage and cost. What is known about the effects of increased STAA vehicle travel on each of the facilities in questionâpavements, bridges, and shoulders and appurtenancesâis summarized in the following sections. PAVEMENTS Pavement service lives are affected by a variety of factors, including vehicle loading (axle loads and tire pressures as well as total vehicle weight), traffic volumes and mix, environment, subgrade conditions, initial pavement design and construction, maintenance, and pavement age (TRB 1986, 159). Research on pavement performance has been focused mainly on the relationship between vehicle loads and pavement design to explain pavement deterioration; far less is known about the effects of environment, maintenance, or other vehicle characteristics such as suspension and tire pressure, or the interaction of these factors, on pavement. Models of Pavement Deterioration The best known research on pavement damage, which was conducted by the American Association of State Highway Officials (AASHO), now AASHTO, was completed in the early 1960s (Highway Research Board 1962). The research involved a test of the performance of the two basic pavement types, flexible and rigid,1 under controlled traffic conditions for different traffic volumes and vehicle types and loads, including tractor- semitrailers. The test did not examine the effects of different environmen- tal conditions or maintenance practices and was limited to the truck configurations typical of the late 1950s. Although considerable research has been conducted to address the limitations of the AASHO Road Test (see Rauhut 1988 for a summary of ongoing research efforts), it is still the most widely used' and accepted method of analyzing the effects of different loading scenarios'on pave-
Highway Condition 173 ment condition. A recent effort to extend the AASHTO pavement model to capture the features of today's heavy trucks that were not considered in the AASHO Road Test, such as increased tire pressures, tire type, multiple axles, and new suspension systems, concluded that the factors that have the most significant effect on pavement deterioration continue to be those considered in the initial road test, that is, the loads or weights on individual axles (J. A. Deacon, Kentucky Transportation Center, University of Kentucky, 1988, unpublished data). Thus AASHTO pro- cedures are used in this study to analyze the effects of the longer, wider, and heavier trucks authorized by the 1982 STAA. Measuring Pavement Deterioration The most important factors in evaluating the effect of changes in vehicle size and weight on pavement deterioration are vehicle loadings and vol- umes. All else being equal, what effect will changes in vehicle mix, loads, and volumes have on pavement condition? Pavements are designed to accommodate a projected number of axle load repetitions of a specified magnitude for a projected service life (R. J. Hansen Associates, Inc. 1979, 7). To simplify design procedures, pave- ment design methods typically express the damage created by mixed traffic loads in terms of a base or reference axle load. Formulas developed from the AASHO Road Test,2 for example, allow the conversion of projected axle loads from different vehicle configurations into an equiva- lent number of 18,000-lb single axle loads (AASHTO 1986, 1-9). These equivalent single axle loads (ESALs) are the basis for determining the thickness of the pavement structure required to provide the desired design life (Western Highway Institute 1980, 29) and thus its cost. The AASHTO design procedures indicate the effect of traffic loads on pavement condition. As Figures 8-1 and 8-2 show, the relationship be- tween axle load and pavement life is a power function. The effect of a single axle on flexible or rigid pavement increases as approximately a fourth-power function of axle load. For example, although a 36,000-lb single axle load is only twice as large as an 18,000-lb single axle load, it causes 17 times more loss in pavement life. Spreading a load on single axles, which are typical of twin trailer trucks, rather than on tandem axles [a tandem axle is a pair of closely spaced axles, typically about 4 ft apart (TRB 1986, 215)], which are typical of tractor-semitrailer configurations, is more damaging to flexible pavements but slightly less damaging to rigid pavements for an equivalent load (Figures 8-1 and 8-2). Because of the power function relationship of axle weights, heavy
1.5 Tandem axle 0 . 10 20 30 34 AXLE LOAD (lb x 1.000) 2.0 1.0 load spread o single axles w w > 2 0.5 0 10 20 30 34 AXLE LOAD (lii x 1,000) FIGURE 8-1 Effect of axle load on life of flexible pavement; equivalency factors based on a structural number of 3 and a terminal serviceability value of 2.5 (TRB 1986, 162, 163). FIGURE 8-2 Effect of axle load on life of rigid pavement; equivalency factors based on a slab thickness of 9 in. and a terminal serviceability value of 2.5 (TRB. 1986, 162, 163).
Highway Condition 175 trucks are far more damaging to pavement surfaces than are passenger cars. For example, although a fully loaded five-axle tractor-semitrailer weighs the equivalent of about 20 automobiles, the truck causes the same damage as approximately 5,900 cars on an Interstate highway with flex- ible pavement (AASHTO 1986, Appendix D). Thus, if heavy truck traffic is forecast on a highway, it is critical that the road be designed to accom- modate the heavier axle loads. Changes in truck size and weight regulations, which increase axle loads, will also increase pavement costs. The largest costs will result from the reduction of service life of existing pavements. The effects will be twofold. First, as Figure 8-3 shows, heavier axle loads will result in more rapid ESAL accumulations and thus shorten the interval before pavement resurfacing will be required to maintain desired serviceability levels and increase the present value of the expenditure by moving it forward in time (see Appendix F). The solid lines on the graph represent the original planned 20-year resurfacing cycle. The dashed lines show the effect of an increase in load limits, which is to reduce the service life of the original pavement and thus make overlays needed on a shortened schedule. Second, at the time resurfacing is required, the thickness of the overlay will have to be increased or subsequent resurfacing intervals shortened; however, neither of these costs as much as the first shortened overlay schedule. (The latter effect is shown in Figure 8-3.) In addition to the impacts on pavement service life, increasing axle loads may also increase the level of maintenance required between major resurfacings. Increasing axle loads will also affect the cost of new pavements. Where STAA truck travel is projected, new pavement designs will have to 1st Overlay 2nd Overlay Vi + Increased 1 I 0 1 1972 1983 1990 1992 2000 2005 2010 YEAR FIGURE 8-3 Effect of increased axle load on pavement resurfacing cycle (Illinois DepartmeM of Transportation 1985, 14).
176 PROVIDING AccEss FOR LARGE TRUCKS incorporate thicker pavement surfaces if the heavier loads are to be accommodated without reducing desired pavement life. Impacts of STAA Vehicles on Pavement Life: An Example The 1982 STAA authorized commerical vehicles of greater width and length than had been legal in some states before passage of the act (see Chapter 2). STAA vehicles now account for the majority of new trailer sales as carriers and shippers take advantage of the added capacity pro- vided by the larger equipment. The purpose of this section is to illustrate the probable magnitude of the loss of pavement life and the resulting increased costs to state and local highway departments that result from substituting STAA vehicles for the smaller equipment of pre-STAA di- mensions on a typical access road. Although vehicles that had dimensions the same as or similar to those authorized by the 1982 act were allowed to travel widely in many states, this example focuses on a situation more typical of eastern states in which the longer, wider vehicles were prohib- ited before passage of the act. The main source of increased pavement deterioration is the additional weight of the STAA vehicle. Because of added trailer capacity, and thus payload weight, and slightly greater tare (i.e., empty) weight, the longer tractor-semitrailers and twin trailer trucks weigh more, on average, than the smaller 45-ft by 96-in. tractor-semitrailers they replace. Both vehicle types, however, are constrained by the same axle load and gross vehicle weight limits.3 Table 8-1 gives the differences in tare and payload weights for three of the most common STAA vehiclesâthe 48-ft and 53-ft tractor- semitrailer and the twin trailer truckârelative to the 45-ft tractor-semi- trailer they replace. Payload weights are calculated assuming that the vehicles are loaded to their full cubic capacity with commodities of the same density. Twin trailer trucks have two features in addition to weight that can accelerate pavement deterioration. First, because the cargo is divided between two trailers, it is less likely to be evenly distributed over the axles than in single semitrailers, and this uneven loading causes greater loss of pavement life (TRB 1986, 160). Second, twins have a different axle arrangement than do tractor-semitrailers. They operate with five single axles rather than with the common single and two tandem axles of the tractor-semitrailer (TRB 1986, 160). As Figure 8-1 shows, on flexible pavements equivalent loads cause more loss of pavement life if they are
Highway Condition 177 TABLE 8-1 SIZE AND WEIGHT OF DESIGN VEHICLES Trailer Length Vehicle Tare Vehicle Payload Gross Vehicle (ft) Weight" (lb) Weight" (lb) Weight (lb) 45 26,500 31,000 57,500 48 26,900 35,000 61,900 53 27,600 39,000 66,600 28 (two) 29,500 42,000 71,500 "Tare weight refers to the empty weight of a vehicle. Tare weight figures were taken from Western Highway Institute data (1980, 36) adjusted to reflect the added length and width of STAA combinations. bAssumes vehicles are loaded to volumetric capacity with low-density (i.e., 10 lb/ft3) commodities without exceeding current total gross vehicle weight or axle load limits. Cubic capacities of the four design vehicles are assumed to be 3,100, 3,500, 3,900, and 4,200 ft3, respectively. spread on two single axles than if they are carried by a tandem axle. Although the converse is true for rigid pavements, the differences are not as large. To examine the effect on pavement condition of the STAA twin trailer truck and longer tractor-semitrailer relative to the vehicles they replace, procedures recommended by AASHTO were used to analyze the relative pavement deterioration caused by the design vehicles described in Table 8-1. The analysis is not intended to be representative of all vehicle sizes and weights but to reflect the magnitude of the effects under a simplified scenario. The analysis rests on several simplifying assumptions. First, gross vehi- cle weights for the baseline vehicle (i.e., the 45-ft tractor-semitrailer) and the now common 48-ft tractor-semitrailer were selected from national truck weight data to represent the mean weight for five-axle tractor- semitrailers (unpublished weight distribution summaries for loaded vehi- cles from Federal Highway Administration annual truck weight data, 1984-1987). Second, each vehicle is assumed to be loaded to its full volumetric capacity with commodities of the same density. Finally, car- riers and shippers are assumed to take full advantage of the added capacity of STAA vehicles, and thus the loading equivalents for each vehicle are adjusted, relative to the baseline vehicle, to reflect the re- duced vehicle-miles that will be traveled using the larger equipment. Although vehicle weights may be overstated by assuming full vehicle
178 PROVIDING ACCESS FOR LARGE TRUCKS loading, this effect should be offset to some extent by the simplifying assumption of full use of the added capacity of STAA vehicles. Damage Analysis Table 8-2 gives a summary of the incremental damage, expressed as load equivalencies, caused by the three STAA vehicles to flexible and rigid pavements. The greatest damage relative to the baseline tractor-semi- trailer is caused by the fully loaded twin trailer truck, even after adjust- ment has been made for the reduced miles traveled because of its higher payload capacity. Relative to the baseline vehicle, the twin trailer truck contributes between three-fourths and two and one-half times more ESALs depending on pavement type. The 53-ft tractor-semitrailer con- tributes between one-third and one-half more ESALs than the baseline vehicle. That the larger STAA tractor-semitrailer causes less damage than the twin trailer truck is not surprising because only one factorâincreased weightâaffects the performance of the former whereas distribution of weight and axle arrangement are additional factors that may affect the performance of the latter.4 As the data in the table indicate, the results differ by pavement type. l'win trailer trucks cause proportionately more damage to flexible than to rigid pavements because of the distribution of loads on single axles, which, as mentioned previously, causes more damage than spreading the load on tandem axles. The reverse is true for the tractor-semitrailers, which carry the loads on tandem axles that are more damaging to rigid pavements, although the increase in damage is not as large. For the purposes of this analysis, the main concern is flexible pavements because a majority of truck access routes (i.e., four-fifths of rural and urban arterials) have flexible surface courses (Highway Statistics 19871988, 138, 140, 141). Cost Analysis The preceding analysis showed that, because of the power function rela- tionship between pavement deterioration and axle loads, when fully loaded with a commodity of the same density, STAA vehicles cause greater pavement damage than do the smaller combination vehicles they replace, even after adjustment has been made for the reduction in miles traveled because of higher payload capacity. A key question is what effect this incremental damage will have on pavement costs if STAA vehicles are allowed to travel widely off the National Network.
TABLE 8-2 AXLE LOAD ANALYSIS Axle 1 Axles 2 & 3 Axles 4 & 5 Adjustment Percentage Trailer Length Load Load Load Total Factor for Adjusted Change from (ft) (kips) ESAL' (kips) ESAL (kips) ESAL ESALs Added Capacityc ESALs Base Case Flexible Pavement 45 9.3 0.095 25.6 0.399 22.6 0.255 0.749 1.00 0.749 48 9.3 0.095 27.4 0510 25.2 0.378 0.983 0.89 0.875 +17 53 9.4 0.098 29.4 0.657 27.8 0.535 1.290 0.79 1.019 +36 28 (two) 9.4 0.098 17.6 0.929 14.2 0.424 2.549 0.74 1.886 +152 16.3 0.699 14.0 0.399 - Rigid Pavement 45 9.3 0.065 25.6 0.586 22.6 0.349 1.000 1.00 1.000 48 9.3 0.065 27.4 0.782 25.2 0.551 1.398 0.89 1.244 +24 53 9.4 0.067 29.4 1.053 27.8 0.827 1.947 0.79 1.538 +54 28 (two) 9.4 0.067 17.6 0.921. 14.2 0.367 2.359 0.74 1.746 +75 16.3 0.663 14.0 0.341 Loading factors are based on unpublished FHWA computer printouts of national truck weight data averaged for 1984 through 1987. bAssumes terminal serviceability value = 2.5, pavement strucutral number = 3, and slab thickness = 9 in. cAdjustment factor = 1/(payload weight of higher-cube vehicle/payload weight of base case vehicle).
180 PROVIDING ACCESS FOR LARGE TRUCKS Methodology To address this question, the effect of substituting different numbers of STAA vehicles in the traffic stream was investigated for a typical access highway. A rural principal arterial highway, with a volume and mix of traffic representative of this class of highway, was selected.5 A flexible pavement was assumed because a majority of major arterials fall into this category. Table 8-3 gives a summary of the traffic composition, expected traffic volume over a 12-year pavement design life, and corresponding load equivalencies for this typical highway. As the data in the first column indicate, passenger vehicles account for the largest share (two-thirds) of the traffic, but large combination vehicles that account for 6.4 percent of the traffic are also present.6 These combination vehicles account for a disproportionate share (70 percent) of the pavement damage expressed in ESALs (see last column of Table 8-3). Although this type of highway may not be representative of all access roads, it does reflect the likelihood that STAA vehicles are traveling on highways that have experienced some degree of heavy vehicle traffic. As was pointed out in Chapter 5, one-third of all combination vehicle travel is on major undivided highways. To examine the incremental costs of increasing STAA vehicle travel, TABLE 8-3 AXLE LOADINGS FOR A RURAL ARTERIAL HIGHWAY Vehicle Type Current Traffid' Design Traffid' ESAL Factor" Design ESALs Passenger car 4,270 18,702,600 0.0004 7,481 Single-unit truck 1,814 7,945,320 0.0736 584,776 Combination truck 416 1,822,080 0.749 1,364,738 Total 6,500 28,470,000 1,956,995 "Total traffic volume is based on the median average daily traffic for rural principal arterials as reported in Highway Statistics 1987 (1988, 150). Traffic distribution by vehicle type is based on 1986 data for rural arterials on which 65.7 percent of vehicle- miles are traveled by passenger cars; 27.9 percent by single-unit trucks; and 6.4 percent by combination trucks (Highway Statistics 1987 1988, 171). bCurrent traffic figures are multiplied by 365 to obtain annual equivalents and then by 12 to obtain projected travel for the expected 12-year service life of the pavement. 'ESAL factors for passenger vehicles assume two 2,000-lb single axles. Factors for single-unit trucks are from national truck weight summaries (Kent and Robey 1981, 181). Factors for tractor-semitrailers assume traffic is composed of 45-ft tractor- semitrailers, with average gross vehicle weight of 57,500 lb and ESAL factors from Table 8-2. All ESALs are based on flexible pavements.
Highway Condition 181 pavement rehabilitation costs were first established for the base case scenario using the methodology described in Appendix F. Then the effects of substituting different volumes of STAA twin trailer and longer tractor-semitrailer truck traffic were analyzed for three likely alterna- tives. The first alternative assumes that 10 percent of the 45-ft tractor- semitrailers will be replaced with STAA twin trailer trucks. Currently, about 6 percent of travel by twins occurs on major arterials off Interstate highways (see Chapter 4); the interviews with carriers, summarized in Chapter 4, suggest that twins will continue to be used primarily by less- than-truckload carriers, which account for a small segment of intercity freight movements; thus twins are unlikely to represent much more than 10 percent of total combination vehicle travel in the near future. The second alternative assumes that 20 percent of the 45-ft tractor- semitrailer traffic will be replaced with 53-ft tractor-semitrailers, and 60 percent with the more common 48-ft tractor-semitrailers. Although nei- ther of these vehicles is as damaging as the twin trailer truck, both are likely to be used more widely. The more damaging 53-ft tractor-semi- trailer, however, will be used primarily by carriers of low-density, light- weight freight, which, as discussed in Chapter 4, is not likely to represent more than 20 percent of all combination vehicle traffic.7 The third, and worst case, alternative combines the previous two and assumes that all but 10 percent of the baseline 45-ft tractor-semitrailer truck traffic will be replaced with twin trailer trucks and longer tractor- semitrailers. Results Tables 8-4 and 8-5 give summaries of the results for each of the three alternatives based on the methodology described in Appendix F. As the data in the tables indicate, the worst case results in a 23 percent increase in ESALs, an 18 percent loss in pavement life, and a 15 percent increase in pavement costs. This cost is the result of moving forward the next re- quired resurfacing from 9 to 7.4 years and increasing pavement overlay thickness from 3.92 to 4.17 in.8 Thus, for a highway that has been designed for a modest level of combination vehicle traffic but has not been available for STAA vehicle access, the introduction of STAA vehicles could increase pavement rehabilitation costs by between 7 and 15 percent. The validity of the cost model is predicated on the assumption that pavement deterioration, and thus the costs incurred by heavy truck travel, is caused primarily by traffic loading rather than by environmental degra-
TABLE 8-4 IMPACTS OF INCREASED VOLUME OF STAA TRAFFIC ON PAVEMENT SERVICE LIFE FOR A RURAL ARTERIAL HIGHWAY Annual Percentage Pavement Percentage ESALs in Increase Service Reduction Design Desin over Lifec from Scenario ESALs Lane Base Case (years) Base Case Base case: 45-ft tractor-semitrailers 1,957 81,540 9.03 Case 1: Substitute twin trailer trucks for 10% of CTTd 2,166 90,260 10.7 8.16 9.6 Case 2: Substitute 48-ft tractor-semitrailers for 60% of CT!' and 53-ft tractor-semitrailers for 20% of CTT 2,193 91,380 12.1 8.06 10.7 Case 3: Case 1 plus Case 2 2,402 100,095 22.8 7.36 18.5 See Table 8-3. bDesign ESALs are divided by 12 and then by 2 to find the annual ESALs in the design lane, one of the required inputs for the pavement rehabilitation cost model. Calculations are based on methodology described in Appendix F. = combination truck traffic.
TABLE 8-5 IMPACTS OF INCREASED VOLUME OF STAA TRAFFIC ON PAVEMENT REHABILITATION COSTS FOR A RURAL ARTERIAL HIGHWAY Present Worth of Annual Percentage Rehabili- Percentage Design ESALs in Increase tation Increase ESALs" Desin over Base Costa over Base Scenario (000) Lane Case ($000) Case Base case: 45-ft tractor- semitrailers 1,957 81,540 145.3 Case 1: Substitute twin trailer trucks for 10% of CVI" 2,166 90,260 10.7 156.0 7.4 Case 2: Substitute 48-ft tractor-semitrailers for 60% of CT!' and 53-ft tractor-semitrailers for 20% of CYl' 2,193 91,380 12.1 157.2 8.2 Case 3: Case 1 plus Case 2 2,402 100,095 22.8 166.7 14.7 "See Table 8-3. bDesign ESALs are divided by 12 and then by 2 to find the annual ESALs in the design lane, one of the required inputs for the pavement rehabilitation cost model. cThese costs represent the present worth (at a 7 percent discount rate) of a recurring 12-year cycle of pavement rehabilitations stretched indefinitely into the future (see Appendix F for more details). dç_ç = combination truck traffic.
184 PROVIDING ACCESS FOR LARGE TRUCKS dation. This assumption was tested in developing the model by examining a range of environmental conditions and the pavement serviceability loss associated with them.9 The results indicated that the incremental rehabili- tation costs resulting from increased traffic loading increased only mod- estly as environmental wear intensified (Appendix F). Thus, for all practi- cal purposes, environmental wear can be ignored in assessing the incremental costs of changes in truck size and weight on pavement reha- bilitation costs. A complete assessment of the impact of extending access to STAA vehicles where they have been prohibited should also take into account their effect on costs of maintenance and new pavement construction. The incremental costs, however, are likely to be small relative to pavement rehabilitation costs. Maintenance spending is likely to be compressed as the resurfacing cycle is shortened, thereby increasing the present worth of annual maintenance expenditures. Where STAA vehicle traffic is pro- jected, new pavements should be designed with greater thickness to accommodate these vehicles without reducing desired pavement life; the added cost should increase total paving costs by 2.5 percent.1° Sensitivity Analysis The results provided in the example are sensitive to assumptions about existing traffic loads, present pavement condition, and the projected mix and volume of STAA vehicle traffic on access highways. Existing traffic loads clearly affect incremental costs: the marginal cost of pavement rehabilitation (measured in cents per added ESALmile) is much greater on'roads designed for light traffic than on roads designed to accommodate heavy truck traffic (Appendix F). Thus, to the extent that STAA vehicles re likely to travel on roads that currently have some combination vehicle traffic, the incremental cost of pavement rehabilitation will not be as great as it would be if these vehicles operated on roads that were designed only for passenger vehicle traffic. Current pavement condition also affects rehabilitation costs. The incre- mental cost of increasing heavy truck traffic, and thus traffic loads, will reflect the current condition of the pavement, its remaining service life, and the actual increase in axle loadings attributable to STAA vehicles. Various combinations of these factors will result in different incremental costs. Assumptions about the volume of STAA traffic on access highways and the weight of loads will also affect incremental pavement costs. For- tunately, twin trailer trucks, which have the potential to cause the greatest
Highway Condition 185 increase in pavement damage, represent a relatively small share of total combination vehicle travel. Moreover, as discussed in Chapters 4 and 5, the majntityiif travel by twins is on Interstate highways, particularly in those eastern states where access policies are most restrictive. Interviews with carriers and shippers indicate that, depending on the weight of the commodities carried, some carriers may not be able to take full advantage of the added cubic capacity of STAA vehicles because of total gross vehicle weight and axle load constraints. Moreover, because of service demands, not all carriers will be operating fully loaded on each trip, even if axle load and total vehicle weight limits are not a constraint. Pavement Rehabilitation Costs that Result from Extending Access In Chapter 4, a rough estimate was made of the incremental costs of access regulations to the major users of STAA vehicles. Approximately 5 percent of the 27 billion miles traveled annually by these users was estimated to be adversely affected by access restrictions; carriers contin- ued to use 45-ft tractor-semitrailers on these trips. Here an attempt is made to estimate the probable incremental pavement rehabilitation costs if access restrictions are relaxed and these 1.35 billion vehicle-miles are traveled by STAA vehicles. The ESAL factors derived in Table 8-2 are used to compare the addi- tional ESALs generated by combination vehicle traffic composed largely of STAA vehicles (Case 3, Table 8-5) and the ESALs generated by combination vehicle traffic composed of 45-ft tractor-semitrailers (Base case, Table 8-5). These ESAL-factors are 0749for-a:45-fttractot-semi trailer and 0.993 for combination vehicle traffic composed of 10 percent STAA twin trailer trucks, 60 percent STAA 48-ft tractor-semitrailers, 20 percent 53-ft tractor-semitrailers, and 10 percent 45-ft tractor-semi- trailers. ESAL-mile costs were derived from the pavement rehabilitation cost model (see Table 8-5). The annualized cost of the present worth of rehabilitating a 1-mi stretch of pavement on a 12-year cycle recurring indefinitely into the future is $10,171 [$145,300 x 0.07 (the discount rate)]. These pavement costs are based on 163,080 annual ESALs (81,540 ESALs x two lanes) (Table 8-5). Thus the ESAL cost per mile of highway it6.2 cents7($10,171/163,080). These ESAL factors and costs can then be applied to the 1.35 billion vehicle-miles that it is assumed would be traveled by STAA vehicles were they granted access. Each vehiclemile traveled bya45-fLtractor-semi- --------------- -
186 PROVIDING ACCESS FOR LARGE TRUCKS trailer generates 0.749 ESAL at a cost of_6.2centsperESAL-milefor a Sübtituting the higher ESAL factor associated with STAA vehicles, 0.993, and applying the same ESAL-mile cost results in a total cost of $83.1 millionâa $20.8 million increase in total pavement rehabilitation costs if STAA vehicles are granted access on these roads. It could be argued that only a portion of these 1.35 billion vehicle-miles would be traveled off the National Network on access roads constructed to lower design standards. (The productivity calculations assumed 'that, if access were restricted, the entire trip would be made with smaller equip- ment.) If only 40 percent of these trips or vehicle-miles are on major arterial and local highways (as the national travel survey discussed in Chapter 5 indicated), then only 540 million vehicle-miles of travel would be affected." Applying the same ESAL factors and costs as before results in an estimate of $33.2 million, or an $8.1 million increase, in pavement rehabilitation costs on these roads if STAA vehicles are granted access. Thus the pavement rehabilitation cost increases attributable to relaxing access regulations on arterial highways from which STAA vehicles were previously prohibited could range from $8.1 million to $20.8 million, based on the foregoing assumptions. As was true of industry costs, pavement costs are concentrated in those eastern states where access is most restricted. Related Research Several studies that have attempted to assess the impact of STAA vehicle travel on pavement costs have found smaller incremental costs than the example provided in this chapter. In Twin Trailer Trucks it was estimated that if twin trailer trucks accounted for 11 percent of heavy combination vehicle traffic nationwide, the annual incremental pavement costs would be $50 million or approximately 2 percent of total highway rehabilitation expenditures by the states (TRB 1986, 169). Although the study exam- ined the effects on pavement of operating 48-ft tractor-semitrailers, na- tionwide estimates of the incremental pavement costs were not projected. The truck size and weight study prepared in anticipation of the 1982 STAA found that eliminating state restrictions on twin trailer truck travel on Interstate and other Federal-Aid primary highways and imposing nationally uniform weight limits12 would result in a 4 percent annual increase in pavement maintenance and overlay costs on Federal-Aid highways (U.S. DOT 1981, V-33). The costs were based on maintenance and overlays that would be needed to maintain the current condition of the nation's Federal-Aid highways (U.S. DOT 1981, 11-15).
Highway Condition 187 At least one study (Ervin and Gillespie 1986) has been focused on the effects on pavement of increased travel by the longer STAA tractor- semitrailers. The impact on pavement deterioration and rehabilitation costs, using AASHTO loading equivalencies, of operating various trac- tor-semitrailers with trailer lengths ranging from 45 to 53 ft was examined. A 53-ft unit could carry 18 percent more freight of equivalent density than can a 45-ft tractor-semitrailer but would increase pavement deterioration by as much as 34 to 45 percent on flexible and rigid pavements, respec- tively (Ervin and Gillespie 1986, 29-31).' The study attempted to translate the incremental pavement damage into added maintenance costs for highways in Michigan. Although the 48- ft tractor-semitrailer was used as the baseline vehicle, the same methodol- ogy can be applied using the 45-ft tractor-semitrailer as the baseline vehicle (Ervin and Gillespie 1986, 32-34). For each 1 percent of 45-ft tractor-semitrailers replaced with 53-ft tractor-semitrailers, the incre- mental annual rehabilitation cost would range from $1.8 million to $2.9 million depending on payload weight. If 53-ft tractor-semitrailers were to account for 20 percent of all combination vehicle travel in Michigan, the assumption used in the pavement analysis example (see Tables 8-4 and 8-5), then the incremental pavement cost attributable to the 53-ft tractor- semitrailers would represent between 6 and 9 percent of the total pave- ment repair bill attributable to all combination vehicle travel in the state. Summary National and state studies of the impacts of changes in commercial vehicle size regulations on pavement costs have found incremental rehabilitation and maintenance costs ranging from 2 to 9 percent. The studies, however, have been focused mainly on Interstate and other Federal-Aid primary highways and thus have not concentrated on the effects on pavement of STAA vehicle travel on access roads. To illustrate the probable loss of pavement life and increased pavement rehabilitation costs resulting from the introduction of STAA vehicles on access roads on which such travel has been prohibited, an example was developed for an arterial highway typical of many access roads. The example showed that pavement life could be reduced by between 10 and 18 percent and pavement rehabilita- tion costs increased by between 7 and 15 percent by the introduction of STAA vehicles. The incremental costs for maintenance and new construc- tion were not considered, but their effect is likely to be small. It was estimated that relaxing access regulations and allowing STAA vehicles to travel the 1.35 billion vehicle-miles that are now traveled by smaller equipment (see discussion of costs of access to major STAA users
188 PROVIDING ACCESS FOR LARGE TRUCKS in Chapter 4) would increase pavement rehabilitation costs on these arterial highways from $8.1 million to $20.8 million. BRIDGES AND CULVERTS STAA vehicle travel may also affect the condition of the nation's bridges and culverts on access roads. The introduction of STAA vehicles was not accompanied by changes in federal load limit maximums; but, compared with the vehicles they replace, STAA vehicles are heavier on average and transfer their loads to supporting structures differently. Such differences could accelerate bridge and culvert deterioration and reduce service life. Bridges Most U.S. highway bridges are designed to meet specifications developed by AASHTO. These specifications require that bridges withstand stan- dardized loading patterns with a safety factor against collapse; they also require that component steel members and connections be designed to withstand the number of load repetitions expected over the life of the bridge to avoid fatigue failure (AASHTO 1983). The standard loading patterns are hypothetical, but they are intended to cover the effects of in-service trucks loaded to the legal limits. Because legal truck sizes and weights have increased over time, however, AASHTO has periodically amended its standard loadings and guidance about the use of these standards. Currently, AASHTO designates two standard loadings, referred to as the HS-20 and HS-15, for Interstate highways and other highways that are likely to carry heavy truck traffic; most bridges on Interstates and other primary highways were designed for these loadings, and some states design for even heavier loads. However, most bridges on nonprimary Federal-Aid highways were designed for lesser loadings (H-15 or less) (Table 8-6). Although the breakdown of current access roads by functional or administrative classification is not known (see Chapter 3), it is probable that many miles of nonprimary highways are included; it is also probable that many of the bridges on these routes are designed for loadings below the HS-15 or HS-20. State practices of posting or restricting the use of such bridges by heavy trucks differ. For example, some states place no limits on H-15 bridges (other than normal legal limits); others post gross vehicle weight limits below 80,000 lb (U.S. DOT 1981, 111-79). In either case, STAA vehicles will be treated the same as other combination trucks
TABLE 8-6 NUMBERS OF BRIDGES ON FEDERAL-AID HIGHWAYS BY DESIGN LOAD (tabulations from bridge inventory data, U.S. Department of Transportation 1981, 111-75). Highway System HS-20 or Greater HS-15 and H-20 H-15 or Less Other' Total Interstate 38,586 3,952 901 1,002 44,441 (86.8)b (8.9) (2.0) (2.3) (100) Other primary 34,544 19,071 23,476 5,957 83,048 (41.6) (23.0) (28.3) (7.2) (100) Other Federal-Aid 27,240 20,346 42,989 26,951 117,526 (23.2) (17.3) (36.6) (22.9) (100) All Federal-Aid 100,370 43,369 67,366 33,910 245,015 (41.0) (17.7) (27.5) (13.8) (100) Mostly older bridges for which design loads are not known. The load-bearing capacities of these bridges are generally less than HS-20. bNumbers in parentheses are percentages of total.
190 PROvIDIIsJG ACCESS FOR LARGE TRUCKS with the same gross vehicle weights. For access routes the key questions are how do the forces induced in bridges by STAA vehicles compare with those induced by the vehicles they replace, and will the frequency of loading on these bridges change enough to increase fatigue damage? The earlier TRB study of twin trailer trucks compared the forces on bridge superstructures and bridge decks caused by fully loaded (80,000- lb) twins with those caused by fully loaded 45-ft tractor-semitrailers. For the girders, trusses, and floor beams that form the superstructure, the study found that forces induced by twins are either about the same as or less than the forces induced by 45-ft tractor-semitrailers. Similarly, for bridge decks it concluded that the effects of the two vehicles would be approximately the same (TRB 1986, Appendix J). Because their added length spreads the loads further, 48- and 53-ft tractor-semitrailers gener- ally induce smaller forces than equivalently loaded 45-ft tractor-semi- trailers. STAA vehicles with somewhat higher average weights will often re- place existing 40- and 45-ft tractor-semitrailer traffic. Because of the greater payload capacity of STAA vehicles, a smaller increase in truck traffic is likely than otherwise would have been experienced with smaller pre-STAA vehicles, thus mitigating some of the adverse effects of higher average vehicle weights. In some cases, however, an access route that previously had little truck traffic may be made available to and used by STAA vehicles. In such cases older bridges and bridges designed to lower loading standards might experience accelerated deterioration. Overall, the available evidence indicates that the introduction of STAA vehicles will have little differential effect on the service lives of bridges on access roads. Culverts Culverts are pipelike drainage structures that carry surface water beneath highways. They are designed to support the stresses induced by the weight of their earth cover. Traffic loads are a critical factor only when depth of fill is less than about 8 ft (TRB 1986,370). If fill depth is in the range of 2 ft to 8 ft, traffic loading is specified by using a standard truck loading pattern that is similar to the one used in bridge design procedures. Standard design truck loadings that induce stresses at least as severe as those caused by fully loaded twin trailer trucks and the longer STAA tractor-semitrailers are used in designing culverts for roads that are likely to experience heavy truck traffic (TRB 1986, 370). Although the single axles of the twin trailer truck are more destructive than the tandem axles
Highway Condition 191 of the tractor-semitrailers, the effect of the incremental stress is evident only for culverts with fill depths of approximately 2 ft or less, which is atypical of culverts on major highways (TRB 1986, 172-173). Thus, with some exceptions on minor roads, the increased loadings attributable to the introduction of STAA vehicles are unlikely to have a serious adverse affect on the serviceability of properly designed and constructed highway culverts. HIGHWAY SHOULDERS AND ROADSIDE APPURTENANCES The operating characteristics of some STAA vehicles may increase the likelihood of their encroaching onto highway shoulders and the frequency of damage to roadside appurtenances. Highway Shoulders Highway shoulders are constructed from a variety of materials that range from paved surfaces with the same load-bearing capacity as the adjacent traffic lanes to thinly paved, gravel, or turf surfaces. Increasingly, high- way departments are electing to pave shoulders, using a flexible pave- ment, but most are not built to the same design standards as the adjacent travel lanes (TRB 1986, 373). In contrast to vehicles of pre-STAA dimensions, the operating perfor- mance of STAA vehicles poses at least two problems with respect to highway shoulders. First, the additional width of the STAA vehicle may increase the likelihood of encroachment onto shoulders, particularly on narrow two-lane roads, to provide greater clearance from oncoming traffic. In a review of the literature on lane width and vehicle lateral placement, Saag and Leisch (1981) found that drivers of both cars and trucks on opposing lanes use added lane width to increase clearance between vehicles as much as 4 to 5 ft. The implication is that if vehicle width were increased, drivers would be more apt to encroach onto the shoulder than to reduce the amount of clearance between vehicles (TRB 1986, 374). However, Seguin et al. (1982, 8-9) found that, although increases in truck width led to reduced lateral clearance between oncom- ing vehicles and the road edge, shoulder encroachments did not increase as a function of truck width. Second, the added wheelbase length of the STAA tractor-semitrailers may exacerbate the problem of inward offtracking at highway speeds of
192 PROVIDING ACCESS FOR LARGE TRUCKS less than 35 to 45 mph, particularly on two-lane roads with sharp curves (see discussion in Chapter 6). Instead of encroaching onto the oncoming traffic lane, the truck driver is apt to drive onto the shoulder to negotiate the curve. Low-speed offtracking is, however, not a problem for twin trailer trucks, which track better than the 45-ft tractor-semitrailers they replace. More frequent encroachment onto highway shoulders will damage shoulder surfaces that are thinly paved or unpaved. Encroachments by heavy trucks onto shoulders may break up the pavement edge and cause erosion, rutting, and breakup of the shoulder surface itself (TRB 1986, 374). The result may be a severe edge drop condition, that is, a sharp drop in level between the travel lane and the shoulder surface, which causes a hazard and increases the probability of truck rollover if a truck leaves the travel lane (see discussion in Chapter 5). There is no research, however, that suggests the probable magnitude of these effects and the increased maintenance that would be required (TRB 1986, 174). Roadside Appurtenances The operating problems created by the greater length and width of STAA vehicles may also increase the likelihood of contact with and damage to roadside appurtenances. Greater encroachment onto highway shoulders increases the probability of striking guardrails and roadside signs. Guard- rails may not be positioned far enough from the edge of the road to avoid being hit by the inward offtracking at low speeds of the rear trailer wheels of the longer-wheelbase STAA tractor-semitrailers. This problem is par- ticularly evident on sharp horizontal curves and on older interchange ramps. Intersections present particular problems for the longer-wheel- base tractor-semitrailers, which, because of inward offtracking at low speeds, are likely to encroach onto curbs and strike signs, utility poles, or other street hardware placed close to the curb. These problems are not as severe for twin trailer trucks, which, at low speeds, can maneuver better on curves and at intersections than the 45-ft tractor-semitrailers they replace. Little research has been done on increased damage to roadside appur- tenances caused by STAA vehicle travel or the implied increase in rehabil- itation and maintenance costs, which is not likely to be trivial, particularly in urban areas. Roadside barriers, such as guardrails and bridge rails, which are currently designed to contain passenger vehicles, are now being developed with sufficient height and strength to sustain the impact of and redirect heavy trucks. Their high cost, however, will justify their use only at critical locations (Michie 1986, 94). Damage from STAA vehicles at
Highway Condition 193 intersections is likely to involve, as a minimum, curb repair or relocation of curbs and street hardware and, as a maximum, intersection reconstruc- tion. To the extent that offtracking of STAA tractor-semitrailers at inter- sections can be mitigated by regulating the trailer wheelbase as suggested in Chapter 6, the damage and related costs will be reduced. SUMMARY The concern that increased travel by STAA vehicles may accelerate the deterioration of the nation's highways, bridges, and highway appurte- nances has been examined. Highway pavements are quite sensitive to changes in traffic loading because pavement wear increases as a power function of vehicle axle loads. Pavements are designed to accommodate a projected number of axle load repetitions of a certain magnitude over a desired service life. However, if loads are increased by changes in vehicle size and weight, pavement damage accelerates and rehabilitation costs rise as service lives are truncated, and increased pavement thickness is required to avert further damage. STAA vehicles cause greater pavement damage than do the 45-ft tractor-semitrailers they replace, even after adjustment has been made for their greater payload capacity, because of the power function relation- ship between pavement deterioration and heavier axle loads. The twin trailer truck is the most damaging of the STAA vehicles because of its axle spacings and more uneven loading, which, combined with its additional weight, adversely affect pavement life. Fifty-three-foot tractor-semi- trailers are more damaging than are 48-ft tractor-semitrailers, but the effect is not as great as that of twin trailer trucks because the configuration of the longer tractor-semitrailers is essentially the same as that of the 45-ft tractor-semitrailers they replace. The incremental cost of increased pavement damage caused by STAA vehicles, however, depends on the mix and volume of STAA vehicle traffic. An example was provided of the effects of substituting different volumes of STAA vehicles for 45-ft tractor-semitrailers on an arterial highway from which STAA vehicles had been barred but that had been designed for modest levels of combination vehicle traffic. The projected loss in pavement service life ranged from 10 to 18 percent, and the incremental pavement rehabilitation costs ranged from 7 to 15 percent. Other national and state studies found lower pavement cost impacts, but they tended to concentrate on pavement effects on Interstate or other Federal-Aid primary highways, not access roads. It was estimated that the increase in pavement rehabilitation costs attributable to introducing
194 PROVIDING ACCESS FOR LARGE TRUCKS STAA vehicles on those access roads from which the major Users of STAA vehicles are now barred would range from $8.1 million to $20.8 million. The introduction of STAA vehicles is unlikely to have a serious adverse effect on the serviceability of properly designed bridges and culverts on access roads. The forces induced in bridge superstructures and decks by a fully loaded twin trailer truck, the potentially most damaging to struc- tures of all the STAA vehicles, are either the same as or less than the forces induced by a fully loaded 45-ft tractor-semitrailer, the vehicle it replaces. The effect on bridge fatigue of somewhat higher average weights of the larger 1982 vehicles should be partly offset by the smaller increase in truck traffic than would have been experienced with continued use of pre-STAA equipment. Thus the introduction of STAA vehicles generally should have little differential effect on the service lives of bridges on access highways. Increased loadings from STAA vehicles are unlikely to adversely affect the serviceability of culverts except for those with very shallow fill depths on minor highways. The greater width of STAA vehicles and the offtracking problems óaused by increased semitrailer wheelbase length may result in more frequent encroachment onto highway shoulders, particularly on narrow, winding, two-lane roads, and onto curbs at intersections. These encroach- ments are likely to hasten the deterioration of thinly paved or unpaved shoulders, which will create hazardous edge drops. They will probably damage roadside appurtenances, such as signs, utility poles, and guard- rails, that are near the curb or shoulder edge. No research has been conducted on the magnitude of these effects and the implied resultant increase in maintenance and repair bills. NOTES A flexible pavement has a surface layer of asphalt concrete and a rigid pavement has a surface layer of portland cement concrete [U.S. Department of Transporta- tion (DOT) 1981, 111-511. Mason and Dnscoll (1986) provide greater detail in their article on the relation- ships derived from the AASHO Road Test that link pavement performance with load equivalency factors. Pavement condition or performance is measured by the present serviceability index (PSI), which is calculated using a regression equation incorporating such pavement distress variables as longitudinal roughness, rut depth, cracking, and patching. A damage equation estimates the number of 18,000-lb ESALs needed to obtain a specific value of PSI, which includes variables of axle load, axle configuration, and pavement characteristics (Mason and Driscoll 1986, 121, 124). The load equivalency factors themselves are a function, albeit a minor one, of the type of axle group (i.e., single, tandem, or tridem), the load on the axle group, the type of pavement structure (i.e., a measure of thickness), and
Highway Condition 195 the terminal PSI value (i.e., expected remaining service life at the time the pavement needs rehabilitation) (Deacon 1988, 1 and AASH1'O 1986, I-il). These limits are 20,000 lb per single axle, 34,000 lb per tandem axle, and 80,000 lb gross vehicle weight. An analysis conducted for TRB's study, Twin Trailer Trucks (1986, 166) found that approximately one-third of the damage caused to pavements by twin trailer trucks could be attributed to additional weight, one-half to axle arrangements, and the remainder to less uniform weight distribution. Traffic volume and mix were based on national data for rural principal arterial highways reported in Highway Statistics 1987 (1988, 154, 171). For purposes of the example, all of the combination trucks were assumed to be 45- ft tractor-semitrailers of the weights and axle loads described in Tables 8-1 and 8-2. The Truck Trailer Manufacturers Association (1988/1986) reported that 53-ft trailers currently represent 5 percent of all trailer sales. The cost model assumes that the pavement was designed with a structural number of 4 and an expected design life of 12 years, that it is currently in fair to good condition (i.e., a PSI of 3.4), and that rehabilitation will be undertaken when the pavement reaches a PSI of 2.5 and will restore pavement condition to a PSI of 4.2. A minimum overlay of 2 in. is also assumed. Resurfacing costs are based on fixed costs of $90,000/mi and variable costs of $15,000/in/mi. These costs are applied to a two-lane highway with lane widths of 12 ft and shoulder widths of 4 ft and are assumed to recur at 12-year intervals indefinitely into the future. The analysis examined the serviceability loss at the end of a 12-year design life that varied from zero, or no environmental degradation, to one, which reflected envi- ronmental degradation so severe that 60 percent of the total wear for the 12-year rehabilitation cycle could be attributed to environmental factors (Appendix F). A new road with a PSI of 2.6 will require 3.92 in. of paving surface to accommodate 45-ft tractor-semitrailer traffic (i.e., base case, Table 8-4). If all but 10 percent of this truck traffic is replaced by STAA vehicles (i.e., the worst case scenario, Case 3, Table 8-4), then 4.17 in. of overlay is required. At a cost of $15,000/in./mi, this additional 0.25 in. of overlay will cost $3,750/mi and represent a 2.5 percent increase in total paving costs [$90,000 + ($15,000 x 3.92) = $148,800]. This estimate is probably on the low side because some incremental pavement damage and costs would be caused by STAA vehicle travel on Interstate highways. A portion of the pavement cost increase can be attributed to the elimination of lower axle and gross weight limits in seven "barrier" states, which was part of the analysis scenario (U.S. DOT 1981, S-12). These estimates assume a 13.5-lb/ft3 payload that yields an 80,000-lb gross combi- nation vehicle weight with a 53-ft tractor-semitrailer (Ervin and Gillespie 1986, 28). REFERENCES ABBREVIATIONS AASHTO American Association of State Highway and Transportation Officials
196 PROVIDING ACCESS FOR LARGE TRUCKS FHWA Federal Highway Administration HRB Highway Research Board NCHRP National Cooperative Highway Research Program TRB Transportation Research Board U.S. DOT United States Department of Transportation AASHTO. 1986. AASHTO Guide for Design of Pavement Structures. Washing- ton, D.C. AASHTO. 1983. Standard Specifications for Highway Bridges. Washington, D.C. Ervin, R. D., and T. D. Gillespie. 1986. Safety and Operational Impacts of 53- Foot Truck Trailers in Michigan. UMTRI-86-13. University of Michigan Trans- portation Research Institute, Ann Arbor, March, 208 pp. R. J. Hansen Associates, Inc. 1979. State Laws and Regulations on Truck Size and Weight. NCHRP Report 198. TRB, National Research Council, Washington, D.C., Feb., 117 pp. HRB. 1962. The AASHO Road Test, Report 5: Pavement Research. Special Report 61E. National Research Council, Washington, D.C., 352 pp. Highway Statistics 1987. 1988. FHWA, U.S. Department of Transportation. Illinois Department of Transportation. 1985. The Effects of Increased Truck Size and Weight in Illinois. Springfield, July 1, 61 pp. Kent, P. M., and M. T. Robey. 1981. 1975-1979 National Truck Characteristics Report. FHWA, U.S. Department of Transportation, June. Mason, J. M., Jr., and V. S. Driscoll. 1986. Consideration of Larger Trucks in Pavement Design and Management. In Transportation Research Record 1052. TRB, National Research Council, Washington, D.C., pp. 120-128. Michie, J. D. 1986. Large Vehicles and Roadside Safety Considerations. In Transportation Research Record 1052. TRB, National Research Council, Wash- ington, D.C., pp. 90-95. Rauhut, B. 1988. Development of Pavement Load Equivalence Factors Using Predictive Damage Models. Brent Rauhut Engineering Inc., Austin, Tex., Sept., 20 pp. Saag, J. B., and J. E. Leisch. 1981. Synthesis of Information on Roadway Geo- metric Causal Factors. Jack E. Leisch and Associates, Evanston, Ill., Jan. Seguin, E. L., K. W. Crowley, P. C. Harrison, Jr., and K. Perchonok. 1982. The Effects of Truck Size on Driver Behavior. FHWAIRD-81/170. FHWA, U.S. Department of Transportation, March, 138 pp. TRB. 1986. Twin Trailer Trucks. Special Report 211. National Research Council, Washington, D.C., 388 pp. Truck Trailer Manufacturers Association. 1988/1986. Van Trailer Size Report. Alexandria, Va. U.S. DOT. 1981. An Investigation of Truck Size and Weight Limits. Washington, D.C., Aug. Western Highway Institute. 1980. Motor Vehicle Size and Weight Standards: Western Regional Objectives. San Bruno, Calif., July.
Summary. Assessment T HIS CHAPTER CONTAINS THE major findings and recom-mendations for a national policy on reasonable access and the rationale for the recommended approach. The recommenda- tions are based on a review of the technical literature on what is known about the operation of STAA vehicles on access roads relative to the vehicles they replace (Chapters 5 through 8) as well as on an assessment of state highway conditions, existing access policies, and truck operating practices (Chapters 3 and 4). POLICY ALTERNATIVES The study committee examined the feasibility of adopting a uniform standard for access off the National Network as a solution to the problems that the wide disparity in state access policies causes the trucking industry and shippers. This approach had considerable appeal. First, a single standard would replace the existing patchwork of different access policies and practices and thus satisfy the desire of the industry for greater uniformity. Second, a uniform standard would be simple to understand and communicate and easier to enforce. Several different standards, some of which had been identified as methods currently used for regulating access, were reviewed for national application (see Chapter 3). Among the approaches examined were A specified minimum distance from the National Network within which STAA vehicles could travel unrestricted. This approach has been proposed as a national standard by the Federal Highway Administration 197
198 PROVIDING ACCESS FOR LARGE TRUCKS (FHWA) in its notice of proposed rulemaking (Federal Register 1988, 53,009).' Restricting access to certain types of highways [e.g., Federal-Aid primary (FAP) highways] or certain roadway conditions (e.g., roads with lane widths of 10 ft or more). The latter was proposed by the National Industrial Transportation League petition as a criterion for evaluating access requests (Chapter 2).2 Limiting access to the shortest distance between the National Net- work and terminals or facilities for food, fuel, repair, and rest (i.e., service facilities). A review of each of these approaches uncovered technical as well as practical difficulties with adopting a uniform standard for access. A distance limit for access is insensitive to geographic and demographic differences among the states and among regions within states. For exam- ple, limiting access to 5 mi from the National Network in a rural state would still leave many truckload carriers short of their required destina- tions. However, this same 5-mi limit for a city like Philadelphia would open virtually all city streets to STAA vehicles. Defining different mile- age limits for rural and urban areas could alleviate part of the problem, but a mileage limit per Se, which is not based on an evaluation of the road itself, is perceived to be arbitrary and inequitable. Setting the limit at 5 mi implies that the road becomes inappropriate or "unsafe" for access at 5.1 mi and favors those terminals and receivers that are located on the "right side" of the limit. Inadequate technical understanding of the link between safety and highway characteristics as well as state-to-state differences in highway conditions preclude development of an access standard based on highway characteristics or road category. As was concluded in Chapters 5 and 6, the available research on the factors that affect safety simply does not provide an adequate basis on which to make fine distinctions, such as the lane width at which the roadway becomes too narrow for the safe opera- tion of certain vehicles. Twelve-foot lanes allow adequate clearance for a vehicle that is 8.5-ft wide. But what lane width is inadequate for safe operation? 10 ft? 9 ft? And how is an adequate lane width affected by other geometric characteristics? The feasibility of allowing access on certain classes of highways, such as FAP roads, as a proxy for geometric conditions was also considered. However, road conditions vary even within broad highway classifications. Thus, although primary highways function as major connectors between cities and industrial centers, not all primary highways are built to the same standards. In California, for example, some roads on the secondary and
Summary Assessment 199 urban systems have better geometries than primary highways. In addi- tion, even if all FAP roads were open to STAA vehicles, access on other classes of highways would be required to reach terminals and service facilities that are not located on FAP highways. Differences in local highway conditions would also affect an access policy based on the shortest reasonable distance between the National Network and terminals or service facilities. All else being equal, the shorter the distance traveled by large trucks, the less the risk of their being involved in an accident. However, if road conditions differ, the shorter road is not necessarily the safer road. Indeed, some states now require that STAA vehicles take a longer road to their destination in order to avoid a shorter, but less safe, alternate route. In sum, geographic and demographic differences, local variations in highway condition, and the lack of clear and quantifiable criteria for determining safety argued against a single national standard. Moreover, the majority of states has already developed various access policies that accommodate the concerns of government and the needs of industry. Thus the committee concluded that a uniform standard for access would be not only inappropriate but also impractical and recommended instead a more uniform process for identifying highways that are appropriate for access. NEED FOR COMMON PROCEDURES FOR PROVIDING ACCESS Although access problems have been resolved in many states, the variety of approaches identified in the review of state access policies and practices (Chapter 3) provides compelling evidence of the need for state and local governments to adopt a more common approach to evaluating the ade- quacy of their highways for STAA vehicle travel. The surveys and interviews conducted for the study found that access regulations are consistent in neither concept nor implementation. States differ widely in the proportion of mileage that they open to STAA vehicles and in the vehicles that they restrict. Access regulations in many western states are directed toward the longer-wheelbase tractor-semitrailers; in the East, the focus is on twin trailer trucks. Some states have not defined the rationale for their access policies or based their policies on sound safety and engineering considerations. Most local governments with au- thority to establish access policies independently have not done so. How- ever, many local governments have limited resources and technical knowledge about the handling and performance of STAA vehicles, and
200 PROVIDING ACCESS FOR LARGE TRUCKS thus the potential exists for an even wider disparity in access policies at the local than at the state level. Given these findings, the committee concluded that the FHWA should require all states to adopt procedures based on safety and engineering considerations for assessing the adequacy of their highways to accommo- date STAA vehicles. The FHWA should review and certify these pro- cedures; states that already have access policies that satisfy government and industry concerns could petition FHWA for certification of their current procedures. CHARACTERISTICS OF A PROCESS FOR REVIEWING ROADS FOR ACCESS Judgments about the adequacy of highways to provide access for STAA vehicles are best made by reviewing specific candidate highways in rela- tion to the vehicles that will use them. Currently, the District of Columbia and 19 of the 35 states that regulate access have some form of route review for designating highways that are appropriate for access. The study com- mittee identified specific criteria that should be used in evaluating the appropriateness of highways for access and outlined how these criteria should be applied. Definition of Criteria The 1982 STAA provided that states must permit vehicles authorized by the act reasonable access from the National Network to terminals and service facilities but did not preempt the police powers of states to safeguard public safety on roads within their jurisdiction (U.S. House of Representatives Report No. 97-555 1982, 24). Congressional intent was that safety should be the primary reason for denying access. A review of the safety literature and accident data (Chapter 5) found that direct measures of the accident experience of STAA vehicles on different types of roads and under different operating conditions are simply not avail- able. The safety of these vehicles is likely to depend on their handling and performance characteristics, roadway geometry, traffic characteristics, and the driver. The relationships among these factors are not well under- stood and cannot readily be quantified, which complicates the task of determining where STAA vehicles can safely travel.
Summary Assessment 201 However, several critical operating characteristics of STAA vehicles are identified that, in conjunction with certain roadway conditions, could increase accident risk (Chapter 6). The most critical vehicle performance characteristics are offtracking of STAA tractor-semitrailers at speeds below 35 to 40 mph3 and, to a lesser extent, overall truck length (twin trailer trucks are the critical vehicle) and truck width (both vehicles). These operating characteristics can create problems on roads with the following geometric conditions: sharp horizontal curves on two-lane roads and inadequate turning space at intersections (the STAA tractor-semi- trailer is the critical vehicle); limited sight distance for passing and at intersections and at-grade railroad crossings (the longer twin trailer truck is the critical vehicle); and narrow lane and shoulder width (and unim- proved shoulders) and ramps and interchanges that are inadequately designed for large trucks (both twins and tractor-semitrailers can be a problem). Highway engineers should examine the interaction among these factors on potential access roads with poor geometric conditions. To the extent that traffic volume and crash frequency are useful in identifying high- or low-risk locations, these factors may also be considered in making a final judgment about the appropriateness of a highway for access by STAA vehicles. Chapter 6 and Appendix E provide more guidance on how specific vehicle performance characteristics, particularly offtracking, and roadway conditions can be evaluated in making this determination. Although many of the vehicle performance characteristics, such as offtracking, can be quantified for a range of highway conditions, the determination of where to draw the line between "safe" and "unsafe" remains a question of judgment. Roads are not "safe" or "unsafe"; they are merely "more safe" or "less safe." The committee believes that the very process of defining the performance characteristics of STAA vehicles and examining them in relation to the roads on which access is proposed should do much to provide sound evaluation criteria on which to base access policies and a means for their consistent application. Application of Criteria States differ in their resources and capacity to evaluate all of the highways under their jurisdiction with respect to all of the criteria listed. Moreover, many states have already made decisions on access roads that do not reflect the suggested criteria. Thus a two-tiered approach is proposed to balance the need for a thorough evaluation of the adequacy of highways for STAA vehicle travel with the practical concerns just noted.
202 PROVIDING ACCESS FOR LARGE TRUCKS Review of Through- Travel Highways Because of the importance to safety of ensuring that large trucks travel on the best roads (i.e., those designed to the highest standards), states that have limited miles of their FAP highways, or other roads built to equiva- lent standards, on the National Network or on state-designated networks should review other highways to determine if additional mileage can be opened to STAA vehicles. Specifically, states should use the criteria recommended in this report to review all FAP highways not already on such networks as well as other heavily traveled secondary and urban system highways that intersec.t with these networks. States should be particularly aware of the undeniably better safety record of divided highways for all large trucks. This review should not be conducted on a case-by-case basis in response to carrier or shipper requests; it should be initiated and completed by the state and the results reported to the FHWA within a reasonable time. Information provided by state trucking associations, carriers, and ship- pers for this study (Chapters 3 and 4) indicates that opening more through-travel roads in states with relatively limited amounts of FAP mileage available for STAA vehicle travel could contribute greatly to the alleviation of the access problems of industry. States may also wish to use the criteria recommended in this report to review designated highways on which safety problems arise. Access to Terminals and Other Destinations Even if more through-travel miles are made available, STAA vehicles will still need to exit these through-travel networks to reach their final destina- tions. States should evaluate highways for such access, commonly known as terminal access, according to the criteria discussed previously. Because carriers' need for access is virtually unlimited (as discussed in Chapter 5, carriers need to reach a wide range of locations), states may continue to evaluate individual requests for access on a case-by-case basis. However, once a state grants access approval for one type of STAA vehicle, this approval should apply to all vehicles of that type regardless of who owns or operates them. Because most states have already granted many re- quests for terminal access since the 1982 STAA was enacted, the amount of mileage to be reviewed or rereviewed should be manageable.
Summary Assessment 203 Access to Service Facilities States must ensure that carriers have adequate access to service facilities off the National Network and state-designated through-travel networks. Many states now allow STAA vehicles to travel a short distance, generally ranging from 1 to 3 mi, from the National Network to reach service facilities (see Chapter 3). These policies have not been raised as a problem by government or industry. States should continue the policy of providing a distance-based access limit of at least 1 mi to service facilities. Although states may deny access to service facilities on roads that have been identified as inappropriate on the basis of the criteria recommended in this study, it is impractical and of limited value to require states to evaluate all of these short road segments. If access to facilities is denied for engineering or safety reasons, access should be provided to other service facilities within a reasonable distance. REGULATING OFFTRACKING Disagreements between the states and industry over the adequacy of mileage provided for through travel and access by STAA vehicles arise in part because a majority of carriers need to travel to a wide range of destinations, many of them far from the National Network (Chapter 4). Industry cost pressures and logistics are not conducive to keeping two fleets of different sized vehicles, but many access highways as well as some through-travel highways are not built to design standards adequate to accommodate STAA vehicles or, in some cases, most large combination vehicles. Recognizing that it will not be feasible for state and local govern- ments to upgrade all highways with restrictive geometry so that the roadway will "fit" the vehicle, the study committee sought opportunities for extending access and through-travel highways by identifying ways in which the vehicle can be made to "fit" the roadway. Although vehicle maneuverability, measured by the extent of low- speed inward offtracking, is only one of several factors to consider in judging the safety of a road for STAA vehicle travel, it is an important aspect of vehicle performance that is noticeably and measurably different for STAA and pre-STAA vehicles. Inward offtracking can be controlled by proper configuration of the vehicle, and several states regulate the dimensions that most affect offtracking to improve the maneuverability of STAA vehicles on highways with restrictive geometry.
204 PROVIDING ACCESS FOR LARGE TRUCKS Critical Vehicles and Dimensions for Regulation Inward offtracking is a problem for the longer-wheelbase STAA tractor- semitrailer. As discussed in Chapter 6 and Appendix E, the maneu- verability of twin trailer trucks at speeds below 35 to 40mph is better than that of the pre-STAA tractor-semitrailers they replace. The dimension that most affects the extent of low-speed, inward off- tracking is the trailer wheelbase, generally measured from the kingpin to the center of the rear trailer axle or axles. By shortening this distance, offtracking is reduced and the vehicle can maneuver better on curves and at intersections.4 Tractor wheelbase length also affects offtracking but to a lesser extent. At an urban intersection with a 90-degree turn angle and a 60-ft radius, every 1-ft increase in trailer wheelbase length, measured from the kingpin to the center of the rear trailer axle or axles, increases offtracking by 0.60 ft. A similar 1-ft increase in tractor wheelbase length increases offtracking 0.23 ft. A majority of states that currently regulate offtracking focus on the kingpin-to-rear-axle dimension. Recommended Standard for Regulation States that regulate wheelbase dimensions have made different interpre- tations of the provisions of the 1982 STAA with respect to their authority to impose these restrictions on the National Network and its connecting access routes. Congress should clarify whether states have the authority to impose these restrictions on the National Network and its access routes under the provisions of the STAA. A small majority of the committee recommended that states be encour- aged to adopt a maximum kingpin setting of 41 ft, measured from the kingpin to the center of the rear trailer axle or group of axles, on their National Network highways and access routes if Congress indicates that states have this authority. Every effort should be made to expedite FHWA encouragement of state acceptance of this kingpin setting as a criterion for evaluating access routes. Several other committee members proposed stronger action, recommending that states be required to adopt a maxi- mum kingpin setting of 41 ft and that the FHWA be directed to include this setting in the final rulemaking on access. This kingpin setting should also be included in FHWA regulations that apply to National Network highways as well as access routes if Congress indicates that states have the authority to restrict kingpin-to-rear-axle dimensions on these roads. A 41-ft setting was selected as a practical compromise. This setting makes the maneuverability of the longer STAA semitrailers equivalent to
Summary Assessment 205 that of the 48-ft semitrailer with its rear trailer axle or axles in the farthest back position, and nearly equivalent to the pre-STAA 45-ft semitrailer, for a range of highway geometric conditions. The 48-ft semitrailer instead of the 45-ft semitrailer was selected as the standard vehicle for defining offtracking because the former is fast becoming the industry-standard semitrailer. The committee believes that greater attention should be given to the longer STAA semitrailers that are grandfathered by the 1982 STAA or have been approved by state legislatures since the 1982 act because these longer semitrailers exhibit the most severe offtracking problems at low speeds (see Chapter 6-and Appendix E). A 41-ft setting should improve vehicle maneuverability enough to increase the highway mileage that may be considered for through travel and access by STAA tractor-semitrailers, except on roads with very restrictive geometry. Although these roads could be considered for travel by STAA tractor-semitrailers if a trailer wheelbase setting of less than 41 ft were imposed, the intent of the committee is not to encourage a proliferation of different state-required kingpin settings, which could reduce carrier compliance and complicate enforcement. Limitations of Offtracking Regulations Regulating vehicle dimensions is one method of making more mileage available for consideration for through travel and access by the longer STAA tractor-semitrailers, but it is not without limitations. First, there are limits on the extent to which the vehicle can be made to "fit" the roadway by shortening the distance between the kingpin and the center of the rear axle or axles. A short wheelbase on a long van box can result in reduced vehicle stability and a long rear trailer overhang; both of these would reduce vehicle safety. A recent study of the performance charac- teristics of 53-ft tractor-semitrailers recommends a wheelbase dimension of 40.5 ft (measured from the kingpin to the center of the rear trailer axles) as the shortest wheelbase length for this trailer size that would not degrade vehicle stability. However, the study also proposes installation of rear underride guards to mitigate the impact of the long rear trailer overhang (Ervin and Gillespie 1986, iiiâiv). Second, the imposition of offtracking regulations may result in produc- tivity losses for carriers of certain commodities because of axle load limitations. The most advantageous configuration for meeting the bridge formula is a wide separation between the axles to spread the load. Few carriers, however, are likely to be adversely affected by a maximum 41-ft kingpin setting. An analysis conducted by the California Department of
206 PROVIDING ACCESS FOR LARGE TRUCKS Transportation (Caltrans) found that carriers of lightweight commodities (no denser than 11.9 lb/ft) should be unaffected by shortening the kingpin dimension because they "cube out" before they meet load limits (Caltrans 1987, 330_333)â¢5 Carriers of commodities denser than about 13.9 lb/ft3 will "weigh out" at a kingpin setting less than 41 ft (Caltrans 1987, 330-333) and should not be affected by a longer setting. Thus a kingpin setting of 41 ft would only affect carriers of commodities within a relatively small density range. The effectiveness of offtracking regulations ultimately depends on enforcement. Law enforcement officials in special commercial units should be able to identify vehicles that are not in compliance with off- tracking regulations. They are accustomed to measuring the distance between axles to enforce the bridge formula, although these measure- ments are typically taken when the vehicle is stopped at a weigh station or at portable scales; enforcement of wheelbase limits will require law enforcement officials to spot out-of-compliance vehicles as they travel down the highway. State highway police and local law enforcement offi- cers who are untrained in commercial vehicle enforcement are likely to have greater difficulty enforcing offtracking regulations, but this may be true of other aspects of truck access regulation as well. LOCAL GOVERNMENT ACCESS POLICIES All states have enacted access policies that apply to highways under their jurisdiction, but considerable miles of highway are the responsibility of counties, cities, and towns. Local governments in 18 states have the independent authority to establish access policies on highways under their jurisdiction, and in 10 additional states local government input to state access decisions is solicited (Chapter 3). A majority of local governments have not developed access policies related specifically to STAA vehicles; they treat these vehicles as they would all large trucks operating on local roads. Because more local governments may establish access policies in the future, these policies should be based on the same approach that is being recommended for state governments. Many of the local officials interviewed for this study were not familiar with the operating characteristics of STAA vehicles and expressed need for guidance from the state concerning appropriate criteria for evaluating the adequacy of local roads for access. Where multiple reviews (i.e., by state and local governments) of a proposed access road are required, a
Summary Assessment 207 state role in coordinating these evaluations can be critical to ensure a consistent and timely appraisal. States should take a leadership role in providing assistance to local governments on the technical and administrative aspects of devising access policies. They should provide guidance to local governments about the criteria to consider in evaluating access requests, provide technical information about the operating characteristics of STAA vehicles that is pertinent to conducting route reviews, and even conduct the reviews for small local governments with limited technical capacity and resources to do so themselves. States may also coordinate industry requests for access that involve multiple government reviews, establish a time frame for completion of reviews, and create a mechanism for resolving any conflicts over interpretation of evaluation criteria. IMPLEMENTATION OF ACCESS POLICIES The review of current state access policies (Chapter 3) concluded that access policies work best if the review is timely, the policies are clearly communicated to industry and law enforcement officials, and there is a formal mechanism for government and industry to use to resolve prob- lems. Timeliness of Reviews The timeliness of route reviews has been a central issue in at least one of the court cases that have arisen over the question of reasonable access (Chapter 2). In those states in which local governments have independent authority to review requests for access on local roads, a coordinating mechanism such as that previously described could help streamline the review process. States should process applications for continuing access in 30 days or less. If local as well as state reviews are required, the approval process could be extended to 90 days, but access would be automatic if the time limitation were exceeded. These recommendations are based on policies adopted by Pennsylvania that have helped reduce industry con- cern over lack of timely response to access requests in that state. When a state or local government grants access approval to one opera- tor of a type of STAA vehicle, this approval should apply to all vehicles of that type. This recommendation is not intended to supersede state or local permits for a single trip by an oversize or overweight vehicle.
208 PROVIDING ACCESS FOR LARGE TRUCKS Communication and Enforcement of Access Policies Many states have prepared maps, widely available to carriers and ship- pers, that show through-travel networks. These maps also frequently indicate general terminal access policies and any other restrictions on travel, such as offtracking regulations. Because the status of these desig- nated highways and general access policies is unlikely to change fre- quently, such maps should be prepared by all states after they have conducted the previously recommended review of FAP or FAP-equiva- lent highways. Carriers, however, will still need to know where it is legal to exit these major through-travel highways. Truckload carriers, in particular, who travel to a wide range of locations over a wide range of routes on an irregular schedule, need a simple way of knowing which roads they can use. Signing roads with a standard logo would be the simplest method of communicating this information. Because few states currently sign access roads, signs will require new expenditures by most state and local govern- ments that restrict access. For states that have opened the majority of their highways to STAA vehicles, indicating the access roads that are closed to STAA vehicles would require the least expenditure. Alter- natively, states could use signs to identify access roads that are open to STAA vehicles; to minimize costs they could sign the end of access roads with a warning at the nearest intersection as California does. Mechanisms for Negotiating Access Problems States that have established formal mechanisms, such as a government- industry task force, for the negotiation and resolution of access problems have found a marked improvement in communication on access issues. In states with a history of controversy over access policies, such as Pennsylva- nia and Alabama, creation of this kind of forum has been a major factor in resolving disputes over access policies. DEFINITION OF TERMINAL Congress requested that the truck access study provide an appropriate definition of "terminal" as part of developing a national policy on access. The access provisions of the 1982 STAA require states to provide access for vehicles of the dimensions authorized by the act to certain destina- tions, including terminals and service facilities. However, just as the 1982
Summary Assessment 209 STAA did not define "reasonable access," it also did not define "termi- nal." The survey of current state access policies and practices revealed that many states define "terminal" broadly as "point of loading or un- loading"; only 10 states have a more specific definition (Chapter 3). In practice access is rarely denied because the carrier's destination does not meet the state's definition of "terminal." Five of the ten definitions of terminal apply only to access for twin trailer trucks, and LTL terminals nearly always meet the definition. The remaining five definitions apply to STAA tractor-semitrailers as well as twin trailer trucks; their main pur- pose is to prevent the operation of twin trailer trucks as full two-trailer units and the use of longer STAA tractor-semitrailers for making deliv- eries to retail locations in congested urban areas. In theory if, as this study recommends, the determination of the appro- priateness of a highway for access is based on an evaluation of the adequacy of the road to accommodate the vehicle, the destination of the vehicle should not be of concern. The situation, however, is more com- plex. First, eliminating the definition of "terminal" entirely could be perceived as tantamount to opening all carrier destinations to all STAA vehicles, although this need not be the case if thorough route evaluations are conducted. One implication would be that twin trailer trucks operat- ing as full two-trailer units could travel to more destinations than they do now. Second, eliminating the notion of a terminus or destination point on access roads could open these roads to high volumes of through-travel traffic, blurring the distinction between roads built to high standards that have been designated for heavy volumes of through travel (i.e., the National Network and state-designated networks) and roads, generally built to lower standards, that are intended for the more limited purpose of providing access to specific commercial operations. Without some method of distinguishing between these two types of roads, the notion of a hierarchy of roads appropriate for truck travel that is implicit in the concept of the National Network is likely to be lost. A definition of "terminal" is needed to address these concerns. To be equitable, this definition should be broad enough to include any location where (a) freight either originates, terminates, or is handled in the transportation process or (b) carriers maintain operating facilities. How- ever, the decision to provide access to these destinations would still rest on a determination of the adequacy of the road to accommodate STAA vehicles, and states may wish to take a harder look at what roads are appropriate for combination vehicle travel in general as well as for STAA vehicles. The definition of "terminal" provided in this study is not in- tended to supersede existing bans on combination truck travel, such as
210 PROVIDING ACCESS FOR LARGE TRUCKS those on through travel on residential streets or weight-posted roads or bridges. MONITORING THE PERFORMANCE OF STAA VEHICLES One of the difficulties of defining where access for STAA vehicles is appropriate, and where it is not, is the lack of information on the accident experience of these vehicles on different categories of roads. Many state accident reporting systems are beginning to differentiate between twin trailer trucks and other large truck configurations because the difference is readily visible to the officer reporting the accident. However, a vast majority of states do not distinguish vehicle length and width in their accident report forms, nor do many states gather reliable information on truck miles traveled to allow computation of accident rates. Determining the type and level of detail of information that should be gathered for accident analysis without overburdening reporting person- nel is beyond the scope of this study. However, two efforts are currently under way that focus on the issue of state accident reporting. The National Governors Association has established a Committee on Uniform Truck Accident Reporting Among the States to determine a minimum set of common elements that should be incorporated by all states in their accident report forms. A draft final report from the committee should be available close to the time this study is published. The Transportation Research Board's study on Truck Safety Data Needs also addresses the issue of what data collection methods and information are needed to provide an adequate understanding of the safety performance of large trucks; this study is slated for completion by the end of 1989. The truck access committee strongly endorses timely completion of these efforts. CONCLUSION The issue of reasonable access grew out of the concept of a designated National Network of trunk roads for truck travel expressed in the 1982 STAA. The network concept was an attempt to strike a balance between productivity and safety. It would allow the trucking industry and shippers to enjoy the productivity benefits of larger equipment but would mini- mize any adverse impacts on safety and traffic operations by keeping those vehicles on a network of roads designed to accommodate them. The concept breaks down precisely over the issue of the scope of the National Network and access from this network. A vast majority of
Summary Assessment 211 carriers, with the possible exception of the relatively small LTL carrier segment, need to travel broadly to many destinations off the National Network and thus cannot readily be confined to a network of the nation's "best" highways. The clear productivity benefits that result from the use of more efficient equipment create pressure to use this equipment on as many roads as possible, and the difficulty of enforcing restrictions on travel off the National Network when a majority of large trucks simply "go where they have to" encourages wider use of STAA vehicles. Many state and local transportation officials believe that the existing road net- work, particularly access roads built to lower design standards than the Interstate system, is at the limit of its ability to accommodate large trucks. However, they find it difficult to document the impact of incremental increases in truck size on safety and traffic operations, particularly when each increment in size is relatively small and the impacts of larger trucks are mitigated to some degree by the smaller increase in truck travel than would otherwise have been experienced with less efficient vehicles. It is also difficult to identify all of the relevant costs that are implied in a change in vehicle size regulation. Some of the recommendations made in this report, for example, will entail new costs for state and local governments. A national policy for providing access is recommended within the framework of current regulations. The objective is to provide more common procedures for evaluating the adequacy of access roads to ac- commodate STAA vehicle travel, but these measures will not assure full consistency in state policies and the extent of access provided. The com- mittee believes that, if vehicle size regulations are revised in the future, the concept of a designated National Network should be carefully reevalu- ated as an appropriate model for vehicle size regulation and the cost implications more thoroughly considered. NOTES The FHWA-proposed rule, however, does make provision for carriers that need access beyond the minimum 5-mi limit. The proposed regulation would require states to have a process for evaluating access requests for terminals that are farther than the distance limit. One alternative would require states to provide access beyond 5 mi except for safety reasons. The other alternative would provide states greater latitude to reject requests for access beyond the 5-mi limit (Federal Register 1988, 53,009-53,010). The National Industrial Transportation League proposal stated that access could reasonably be denied on posted routes from which large commercial vehicles are generally excluded or to which a safer alternative route exists (Federal Register 1987, 299).
212 PROVIDING ACCESS FOR LARGE TRUCKS At high speeds, the critical vehicle is the twin trailer truck. Here, the problem is less that of offtracking than of vehicle rollover (see discussion in Chapter 6 and Appen- dix E). The latter problem is less likely to occur on access roads on which speeds are lower than on the National Network, but it can occur on access roads with curves on which speeds substantially exceed 40 mph and on ramps and interchanges. Regulating the kingpin dimension requires a van trailer with a slider bogie (i.e., sliding rear axles), a feature that is common on most new van trailers, but that may not be common on other types of vehicles such as tank trucks and autotransporters. Other regulations, such as overall vehicle length, may be required to control offtracking of these vehicles. Because California measures from the kingpin to the rear of the trailer axles, the kingpin dimensions were adjusted so that they approximate the kingpin-to-center- of-rear-trailer-axles setting recommended in this study. REFERENCES ABBREVIATIONS Caltrans California Department of Transportation FHWA Federal Highway Administration Caltrans. 1987. Response to FHWA Docket No. 87-1, Advance Notice of Pro- posed Rulemaking (Federal Register, Vol. 52, No. 2, Jan. 5, pp. 298-300), April 23, pp. 321-333. Ervin, R. D., and T. D. Gillespie. 1986. Safety and Operational Impacts of 53- Foot Truck Trailers in Michigan. UMTRI-86-13. University of Michigan Trans- portation Research Institute, Ann Arbor, March, 208 pp. Federal Register. 1987. Vol. 52, No. 2, Jan. 5, pp. 298-300. Federal Register. 1988. Vol. 53, No. 251, Dec. 30, pp. 53,006-53,012. U.S. House of Representatives Report No. 97-555. 1982. Committee on Public Works and Transportation. 97th Cong., 2d Sess., May 17.
APPENDIX A Federal Legislation Mandating the Truck Access Study Surface Transportation and Uniform Relocation Assistance Act of 1987, Public Law 100-17, 100th Congress, April 2, 1987 (23 USC 101 et seq.) SEC. 158. MOThR VEHICLE STUDY.. STUDY.âThe Secretary shall enter into appropriate arrangements with the Transportation Research Board of the National Academy of Sciences (hereinafterin this section referred to as the "Board") to conduct a study of those motor vehicle issues set forth in subsection (b) of this section. The Board shall consult with the Department of Transportation, the State high- way administrations, the motor carrier industry, highway safety groups, and any other appropriate entities. ITEMS INCLUDED.âThe study shall include an analysis of the impacts of the various positions that have been put forth with respect to each issue. The final report shall include best estimates of the effects on pavement, bridges, highway revenue and cost responsibility, and highway safety, and the changes in transportation costs and other measures of productivity for various segments of the trucking industry resulting from adoption of each of the positions identified and analyzed. Related issues of permitting, weight en- forcement, and data availability and reliability shall be addressed as appropri- ate. The issues to be addressed shall include but not be limited to the following: (1) Elimination of existing, grandfather provisions of section 127, title 23, United States Code, which allow higher axle loads and gross vehicle weights than the 20,000-pound single axle load limit, 34,000-pound tandem axle load limit, and 80,000-pound gross vehicle weight limit maximums authorized by the Federal-Aid Highway Amendments of 213
214 1974 (Public Law 93-643), including permits for divisible loads and statutory provisions providing higher weights by formula, tolerance or statutory specification. Analysis of alternative methods of determining a gross vehicle weight limit and axle loadings for all types of motor carrier vehicles. Analysis of bridge formula contained in section 127 of such title 23 in view of current vehicle configurations, pavement and bridge stresses in accord with 1986 design and construction practices, and existing bridges on and off the Interstate System. Establishment of a nationwide policy regarding the provisions of "reasonable access" to the National Network for combination vehicles established pursuant to the Surface Transportation Assistance Act of 1982. Recommendation of appropriate treatment for specialized hauling vehicles which do not comply with the existing Federal bridge formula. REPORT.âThe Board shall submit a final report to the Secretary and the Committee on Environment and Public Works of the Senate and the Committee on Public Works and Transportation of the House of Representa- tives on the results of the study conducted under this section, not later than 30 months after appropriate arrangements are entered into under subsection (a). Appropriate arrangements shall be concluded within 6 months after the date of the enactment of this Act. AUTHORIZATION OF APPROPRIATIONS .âThere is authorized to be appropriated to carry out this section, out of the Highway Trust Fund (other than the Mass Transit Account), $500,000 per fiscal year for each of fiscal years 1987 and 1988. Funds authorized by this section shall be available for obligation in the same manner and to the same extent as if such funds were apportioned under chapter 1 of title 23, United States Code, and shall remain available until expended. U.S. House of Representatives Report No. 100-498, Conference Report on House Joint Resolution 395, 100th Congress, 1st Session, December 21, 1987, 1131 Motor Carrier Access.âBased on information provided by the Transporta- tion Research Board of the National Academy of Sciences, the conferees believe that the study mandated in Public Law 100-17 on "reasonable access" could be completed within 18 months. The conferees therefore direct the Board to submit within 18 months the report required in section 158(b)(4) of Public Law 100-17. The report on reasonable access should include the definition of "terminal". The Department of Transportation is directed to
215 refrain from issuing a final rule on this issue until after the Board has issued its report. The Department may proceed with its current efforts in this area including soliciting comments from interested parties through a notice of proposed rulemaking. The Department must accord substantial weight to the findings and recommendations contained in the Board report, with safety being the foremost consideration in the rulemaking process. To the extent that the Department's proposed final rule differs from the findings and recommendations of the Board report, the Department must explain fully the reasons for such differences in explanatory material before issuing a final rule. Such material should be provided to the House and Senate Committees on Appropriations and the authorizing committees with jurisdiction over these matters. The conferees encourage the Board to expenditiously complete its work with possible completion as early as 15 months after the date of enact- ment of this Act.
APPENDIX B Sections of Highway Laws Relating to Truck Size Title IV Surface Transportation Assistance Act of 1982, as amended, Public Law 97-424, 97th Congress, January 6, 1983 (49 USC 2311-2313, 2316) PART BâCOMMERCIAL MOTOR VEHICLE LENGTH LIMITATION LENGTH LIMITATIONS ON FEDERALLY ASSISTED HIGHWAYS SEC. 411. (a) No State shall establish, maintain, or enforce any regulation of commerce which imposes a vehicle length limitation of less than forty-eight feet on the length of the semitrailer unit operating in a truck tractor-semi- trailer combination, and of less than twenty-eight feet on the length of any semitrailer or trailer operating in a truck tractor-semitrailer-trailer combina- tion, on any segment of the National System of Interstate and Defense Highways and those classes of qualifying Federal-aid Primary System high- ways as designated by the Secretary, pursuant to subsection (e) of this section. (b) Length limitations established, maintained, or enforced by the States under subsection (a) of this section shall apply solely to the semitrailer or trailer or trailers and not to a truck tractor. No State shall establish, maintain, or enforce any regulation of commerce which imposes an overall length limitation on commercial motor vehicles operating in truck-tractor semitrailer or truck tractor semitrailer, trailer combination. No State shall establish, maintain, or enforce any regulation of commerce which has the effect of prohibiting the use of trailers or semitrailers of such dimensions as those that were in actual and lawful use in such State on December 1, 1982. No State shall establish, maintain, or enforce any regulation of commerce which has the effect of prohibiting the use of existing trailers or semitrailers, of up to 217
218 twenty-eight and one-half feet in length, in a truck tractor-semitrailer-trailer combination if those trailers or semitrailers were actually and lawfully operat- ing on December 1, 1982, within a sixty-five-foot overall length limit in any State. No State shall prohibit commercial motor vehicle combinations consist- ing of a truck tractor and two trailing units on any segment of the National System of Interstate and Defense Highways, and those classes of qualifying Federal-aid Primary System highways as designated by the Secretary pur- suant to subsection (e) of this section. The Secretary is authorized to establish rules to implement the provi- sions of this section, and to make such determinations as are necessary to accommodate specialized equipment (including, but not limited to, auto- mobile transporters) subject to subsections (a) and (b) of this section. (e)(1) The Secretary shall designate as qualifying Federal-aid Primary System highways subject to the provisions of subsections (a) and (c) those Primary System highways that are capable of safety accommodating the vehicle lengths set forth therein. The Secretary shall make an initial determination of which classes of highways shall be designated pursuant to paragraph (1) within 90 days of the date of enactment of this section. The Secretary shall enact final rules pursuant to paragraph (1) no later than two hundred and seventy days from the date of enactment of this section and may revise such rules from time to time thereafter. For the purposes of this section, "truck tractor" shall be defined as the noncargo carrying power unit that operates in combination with a semitrailer or trailer, except that a truck tractor and semitrailer engaged in the transpor- tation of automobiles may transport motor vehicles on part of the power unit. The provisions of this section shall take effect ninety days after the date of enactment of this title. The length limitations described in this section shall be exclusive of safety and energy conservation devices, such as rear view mirrors, turn signal lamps, marker lamps, steps and handholds for entry and egress, flexible fender extensions, mudflaps and splash and spray suppressant devices, load- induced tire bulge, refrigeration units or air compressors and other devices, which the Secretary may interpret as necessary for safe and efficient operation of commercial motor vehicles, except that no device excluded under this subsection from the limitations of this section shall have by its design or use the capability to carry cargo. ACCESS TO THE INTERSTATE SYSTEM SEC. 412. No State may enact or enforce any law denying reasonable access to commercial motor vehicles subject to this title between (1) the Interstate and Defense Highway System and any other qualifying Federal-aid Primary
219 System highways, as designated by the Secretary, and (2) terminals, facilities for food, fuel, repairs, and rest, and points of loading and unloading for household goods carriers. ENFORCEMENT SEC. 413. The Secretary, or, on the request of the Secretary, the Attorney General of the United States, is authorized and directed to institute any civil action for injunctive relief as may be appropriate to assure compliance with the provisions of this title. Such action may be instituted in any district court of the United States in any State where such relief is required to assure compli- ance with the terms of this title. In any action under this section, the court shall, upon a proper showing, issue a temporary restraining order or prelimi- nary or permanent injunction. In any such action, the court may also issue a mandatory injunction commanding any state or person to comply with any applicable provision of this title, or any rule issued under authority of this title. COMMERCIAL MOTOR VEHICLE WIDTH LIMITATION SEC. 416. (a) No State, other than the State of Hawaii, shall establish, maintain, or enforce any regulation of commerce which imposes a vehicle width limitation of more or less than 102 inches on any segment of the National System of Interstate and Defense Highways, or any other qualifying Federal-aid highway as designated by the Secretary of Transportation, with traffic lanes designed to be a width of twelve feet or more; except that a State may continue to enforce any regulation of commerce in effect on April 6, 1983, with respect to motor vehicles that exceed 102 inches in width until the date on which such State adopts a regulation of commerce which complies with the provisions of this subsection. Notwithstanding the provisions of this section or any other provision of law, certain safety devices which the Secretary of Transportation determines are necessary for safe and efficient operation of motor vehicles shall not be included in the calculation of width. Notwithstanding the provisions of this section or any other provisions of law, a State may grant special use permit to motor vehicles that exceed 102 inches in width. Notwithstanding any other provision of law and in accordance with the provisions of this section, a State shall have authority to enforce a commercial vehicle width limitation of 102 inches on any segment of the National System of Interstate and Defense Highways, or any other qualifying Federal-aid highway as designated by the Secretary of Transportation, with traffic lanes designed to be a width of twelve feet or more. The provisions of this section shall take effect on April 6, 1983.
220 Title I Tandem Truck Safety Act of 1984, Public Law 98-554, 98th Congress, October 30, 1984 (49 USC et seq.) SHORT TITLE Sec. 101. This title may be cited as the "Tandem Truck Safety Act of 1984". EXEMPTION FROM LENGTH REQUIREMENTS SEC. 102. Section 411 of the Surface Transportation Assistance Act of 1982 (49 U.S.C. App. 2311) is amended by adding at the end thereof the following new subsection: "(i)(1) If the Governor of a State, after making the consultations specified in paragraph (2) of this subsection, determines that any specific segment of the National System of Interstate and Defense Highways is not capable of safely accommodating motor vehicles having the lengths set forth in subsec- tion (a) of this section or motor vehicle combinations described in subsection (c) of this section, the Governor may notify the Secretary of such determina- tion and request that the Secretary exempt such segment from one or both of such subsections. "(2) Before making such notification, the Governor shall consult with units of local government within the State in which the specific segment of such System is located, as well as the Governor of any State adjacent to that State that might be directly affected by such exemption. As part of such consulta- tions, consideration shall be given to any potential alternative route thatâ can safely accommodate motor vehicles having the lengths set forth in subsection (a) of this section or motor vehicle combinations described in subsection (c) of this section; and serves the area in which such segment is located. "(3) The Governor shall transmit with such notification specific evidence of safety problems that supports such determination and the results of consulta- tion regarding any alternative route under paragraph (2) of this subsection. "(4)(A) If the Secretary determines, upon request by a Governor under paragraph (1) of this subsection or on the Secretary's own initiative, that any segment of the National System of Interstate and Defense Highways is not capable of safely accommodating motor vehicles having the lengths set forth in subsection (a) of this section or motor vehicle combinations described in subsection (c) of this section, the Secretary shall exempt such segment from one or both of such subsections. Before making such determination, the Secretary shall consider any possible alternative route that serves the area in which such segment is located.
221 The Secretary shall make such determination within a period of 120 days after the date of receipt of notification from a Governor under paragraph (1) of this subsection or the date on which the Secretary initiates action under this paragraph, as the case may be, with respect to such segment. If the Secretary determines that such determination will not be made within such time period, the Secretary shall immediately notify the Congress and shall furnish the reasons for the delay, information regarding the resources as- signed, and the projected completion date, for any such determination. The Secretary shall make such determination only after affording interested parties notice and the opportunity for comment. Any exemption granted by the Secretary under this paragraph before the date on which final rules are issued under subsection (a) of this section shall be included as part of such final rules. Any such exemption granted on or after such date shall be published as a revision of such rules." EXEMPTION FROM WIDTH REQUIREMENTS SEC. 103. Section 416 of the Surface Transportation Assistance Act of 1982 (49 U.S.C. App. 2316) is amendedâ by redesignating subsection (e) as subsection (f); and by inserting after subsection (d) the following new subsection: "(e)(1) If the Governor of a State, after making the consultations specified in paragraph (2) of this subsection, determines that any specific segment of the National System of Interstate and Defense Highways is not capable of safely accommodating motor vehicles having the width set forth in subsection (a) of this section, the governor may notify the Secretary of such determina- tion and request that the Secretary exempt such segment from such subsection for the purpose of allowing the State to impose a width limitation of less that 102 inches for vehicles (other than buses) on such segment. "(2) Before making such notification, the Governor shall consult with units of local government within the State in which the specific segment of such System is located, as well as the Governor of any State adjacent to the State that might be directly affected by such exemption. As part of such consulta- tions, consideration shall be given to any potential alternative route thatâ can safely accommodate motor vehicles having the width set forth in subsection (a) of this section; serves the area in which such segment is located. "(3) The Governor shall transmit with such notification specific evidence of safety problems that supports such determination and the results of consulta- tion regarding any alternative route under paragraph (2) of this subsection. "(4)(A) If the Secretary determines, upon request by a Governor under paragraph (1) of this subsection or on the Secretary's own initiative, that any segment of the National System of Interstate and Defense Highways is not capable of safely accommodating motor vehicles having the width set forth in
222 subsection (a) of this section, the Secretary shall exempt such segment from such subsection for the purpose of allowing the State to impose a width limitation of less than 102 inches for vehicles (other than buses) on such segment. Before making such determination, the Secretary shall consider any possible alternative route that serves the area in which such segment is located. The Secretary shall make such determination within a period of 120 days after the date of receipt of notification from a Governor under paragraph (1) of this subsection or the date on which the Secretary initiates action under this paragraph, as the case may be, with respect to such segment. If the Secretary determines that such determination will not be made within such time period, the Secretary shall immediately notify the Congress and shall furnish the reasons for the delay, information regarding the resources as- signed, and the projected completion date, for any such determination. The Secretary shall make such determination only after affording interested parties notice and the opportunity for comment. Any exemption granted by the Secretary under this paragraph before the date on which final rules are issued under subsection (a) of this section shall be included as part of such final rules. Any such exemption granted on or after such date shall be published as a revision of such rules". CONFORMING AMENDMENTS SEC. 104. (a) Section 411(a) of the Surface Transportation Assistance Act of 1982 (49 U.S.C. App. 2311(a)) is amendedâ by striking out "No" and inserting in lieu thereof "Except as pro- vided in subsection (i) of this section, no"; by inserting "(other than a segment exempted under subsection (i) of this section)" after "Highways"; and by striking out "Secretary," and inserting in lieu thereof "Secretary of Transportation (hereinafter in this part referred to as the 'Secretary'),". Section 411(c) of the Surface Transportation Assistance Act of 1982 (49 U.S.C. App. 2311(c)) is amended by inserting "(other than a segment ex- empted under subsection (i) of this section)" after "Highways". Section 412 of the Surface Transportation Assistance Act of 1982 (49 U.S.C. App. 2312) is amended by inserting "(other than any segment thereof which is exempted under section 411(i) or 416(e) of this title)" after "Highway System". Section 4 16(a) of the Surface Transportation Assistance Act of 1982 (49 U.S.C. App. 2316(a)) is amendedâ (1) by striking out "No" and inserting in lieu thereof "Except as pro- vided in subsection (e) of this section, no"; and
223 (2) by inserting "(other than a segment exempted under subsection (e) of this section)" after "Highways". (e) Section 416(d) of the Surface Transportation Assistance Act of 1982 (49 U.S.C. App. 2316(d)) is amendedâ by inserting "(other than a segment exempted under subsection (e) of this section)" after "Highways"; and by striking out "with traffic lanes designed to be a width of twelve feet or more". DESIGNATION OF HIGHWAYS SUBJECT TO WIDTH LIMITATION SEC. 105. Section 416(a) of the Surface Transportation Assistance Act of 1982 (49 U.S.C. App. 2316(a)) is amendedâ by inserting after "more" the second place it appears the following: ", or any other qualifying Federal-aid Primary System highway desig- nated by the Secretary if the Secretary determines thiit such designation is consistent with highway safety"; and by adding at the end of such section the following new sentence: "After the date of the enactment of this sentence, any Federal-aid highway (other than any Interstate highway) which was not designated under this subsection on June 5, 1984, may be designated under this subsection only with the agreement of the Governor of the State in which the highway is located.". REASONABLE ACCESS SEC. 106. Section 412 of the Surface Transportation Assistance Act of 1982 (49 U.S.C. App. 2312) is amendedâ by inserting "(a)" after "Sec. 412."; and by striking out the period at the end of thereof and inserting in lieu thereof the following: "and for any truck tractor-semitrailer combination in which the semitrailer has a length not to exceed 281/2 feet and which generally operates as part of a vehicle combination described in section 411(c) of this Act. "(b) Nothing in this section shall be construed as preventing any State or local government from imposing any reasonable restriction, based on safety considerations, on any truck tractor-semitrailer combination in which the semitrailer has a length not to exceed 281/2 feet and which generally operates as part of a vehicle combination described in section 411(c) of this Act.".
APPENDIX C Quiestionnalres and Detailed Tables for Chapter 3 STATE SURVEY ON TRUCK ACCESS STATE DATE SURVEY RESPONDENT WHO MAY BE CONTACTED FOR CLARIFICA- TION OF RESPONSES TO THIS QUESTIONNAIRE: NAME - TITLE - ADDRESS TELEPHONE DEFINITIONS: STAA Vehiclesâvehicles of the dimensions specified in the Surface Trans- portation Assistance Act (STAA) of 1982 as amended, which include: Twin trailer truck combinations using trailers of up to 28 feet long; Truck tractor-semitrailer combinations using semitrailers up to 48 feet long; Trucks with widths of up to 102 inches. Other specialized equipment as defined. The STAA of 1982 as amended further prohibited states from placing a 225
226 length limit on truck-tractors used in STAA vehicle combinations and from limiting the overall length of STAA vehicles using the National Network (see definition below), and grandfathered longer semitrailers in those states which had accepted semitrailers in excess of 48 feet in length prior to December 1, 1982. National or Designated Networkâthat network of Interstate, Federal-aid Primary, and other specified roads designated by the federal government subsequent to the STAA of 1982 for specific use by STAA vehicles. Access Routesâthose routes which provide access to and from the Na- tional Network to terminals and to facilities for food, fuel, repair, and rest. The 1982 STAA allowed the states to establish their own access policies. I. CHARACTERISTICS OF THE NATIONAL NETWORK AND STATE ACCESS ROUTES Please indicate below the total miles of road* by federal-aid system which have been designated by the federal government in the Federal Register as part of the National Network for STAA vehicle travel. Federal-Aid # Miles on System National Network Total Miles by System Interstate Primary Which, if any, STAA vehicles are allowed unrestricted travel in your state? Please check those below which apply. All STAA vehicles STAA semitrailer combinations STAA twin trailer combinations 102"-wide vehicles Other. Please explain. Has the state designated a supplemental network of routes for truck travel not fully equivalent to the National Network that is subject to vehicle length, width, or vehicle type restrictions? Yes ___ No *Please round off mileage numbers to the nearest whole number. Make your best estimates where precise figures are unavailable, but please indicate that these are estimates.
227 If "Yes," please answer the following questions: Please indicate the mileage of these state-designated, non-equiva- lent routes. __________ miles Please describe the nature of the restrictions. If access is provided from these routes, please describe the access provisions. D. Does the state designate access routes from the National Network (i.e., the routes identified in l.A.) to terminals and to facilities for food, fuel, repairs, and rest? ____ Yes ____ No If "Yes," please answer the following questions. Please indicate the total mileage of access routes. Total miles Please break down this total mileage figure into miles by federal-aid system and number of lanes. If exact figures are not available, please make your best estimate of the mileage in each category. # Miles of # Miles of Access Routes Access Routes Consisting of Federal-Aid Consisting of >2-Lane Total # Miles of System 2-Lane Roads Roads Access Routes Primary Secondary Urban System All Other E. Does the state collect information on the geometric and operating characteristics of its routes to determine the adequacy of roadways to accommodate STAA vehicles? ____ Yes ____ No If "Yes," please check below those characteristics on which the state has information. Lane width Shoulder width and whether shoulder is paved Horizontal curvature (radius and degree) Turning radii at intersections Average daily traffic and traffic composition (% trucks)
228 Other. Please describe II. ACCESS PROVISIONS 1. How does the state define a terminal for the purpose of allowing access by STAA vehicles off the National Network? 2. What are the practical implications of this definition? Briefly indicate your understanding of the state's method of pro- viding reasonable access for those STAA vehicles authorized by the 1982 STAA from the National Network to terminals and to facilities by checking below those categories that apply. (More than one category may apply.) Please enclose a copy of the state's access provisions. Unrestricted (i.e., all STAA vehicles can travel without regard to distance, lane width, or road type) _______ Terminal ______ Facilities Distance-based (e.g., x miles from the National Network) _______ Terminal ______ Facilities By specific route permit or signing of routes _______ Terminal ______ Facilities Combination of (a) and (b) (i.e., access is unrestricted for certain vehicle types, but distance-restricted for other vehicle types) _______ Terminal ______ Facilities Combination of (a) and (c) (i.e., access is unrestricted for certain vehicle types, but restricted by specific route permit or signing for other vehicle types) ______ Terminal ______ Facilities Combination of (b) and (c) (i.e., access is available by permit or signing beyond a general distance-based limit) ______ Terminal ______ Facilities Other ______ Terminal ______ Facilities
229 Briefly describe the rationale for your access policies as defined in II.B. NOTE: If you provide unrestricted access to all STAA vehi- cles, please skip to Question G. Do the state's access rules provide for access by STAA vehicles within a specified number of miles from the National Network for some or all STAA vehicles? If your answer is "No," please skip to question E. If "Yes," please answer the following questions: Are these access provisions established by statute or by ad- ministrative procedure? Please check the box that applies. _______ Statute _______ Administrative procedure What is the mileage access limit for: Length: (Miles) STAA semitrailer combinations (Miles) STAA twin trailer combinations Width: (Miles) STAA vehicle width (i.e., 102-in, wide) Please explain why these distances were selected, partic- ularly if distance of travel allowed differs by vehicle type (e.g., travel by STAA semitrailer combinations is unre- stricted, but STAA twin trailer combinations can only travel x miles from the National Network) Do any other special restrictions apply? (e.g., state routes only, access from designated interchanges only etc.) May truck operators (or terminals or shippers) apply for permission for access beyond the distance limit? ____ Yes ____ No
230 E. Do the state's access rules provide for access by requiring a special permit for operation on or by signing specific routes? If your answer is "No," please skip to Question F. If "Yes," please answer the following questions which apply: Are these access provisions established by statute or by ad- ministrative procedure? Please check the box that applies. _______ Statute _______ Administrative procedure Who can apply for a permit? (e.g., trucking firms, ship- pers, terminals etc.) What information must the applicant supply? (If there is a standard application form, please enclose a copy.) What specific criteria are used to determine if a route is unsuitable for STAA vehicle operation? Once a specific route is approved, either by a permit pro- cess or by signing the routes, who has authority to operate over this route? Please check the items below that apply. Only the party (and its contractors) who submitted the application All vehicles of the type allowed to operate over the route (e.g., all STAA twin trailer combinations) All STAA vehicles Other. Please explain NOTE: If the party who submitted the application is a ter- minal or shipper, what restrictions apply? For how long is the authority to operate an STAA vehicle over a specific route valid? Who is responsible for issuing the permit?
231 Is there any charge for a permit or for route review? ____ Yes ____ No If "Yes," please specify the amount for: First application or review Renewal Since the 1982 STAA went into effect, how many applica- tions for access have been received approved rejected are currently under review What are the, principal reasons for rejecting an applica- tion? On average, how long does it take to process the applica- tion or review a route, including any local government re- views? For those permit applications that have been approved, please indicate below the share of access approvals granted to each of the following facilities: Percent (%) Terminal or other facility of a for-hire carrier (%) Facilities of a shipper operating its own STAA trucks (%) Facilities of a shipper or receiver served mainly by for-hire carriers (%) Public food, fuel, repair, or rest facilities (%) Other. Please describe F If the state does not define access by a prescribed distance from the National Network or by special route permits or sign- ing, please answer the following questions. 1. Please describe and provide a brief explanation of the access policies that are in effect.
232 Are these access provisions established by statute or by ad- ministrative procedure? Please check the box that applies. _______ Statute _______ Administrative procedure Please indicate what specific criteria, if any, are used to de- termine if a route is unsuitable for STAA vehicle operation. Does the state plan any additional restrictions regarding access for longer grandfathered semitrailer lengths? Yes ____ No If "Yes," please explain. Are local governments in the state involved in setting access policies? Yes ____ No If your answer is "No," please skip to Section III. If "Yes," please specify the role of local governments by checking below the items which apply. The state sets access policies and makes the final deci- sion on access, but local governments have input by re- viewing access requests on local routes over which they have jurisdiction. Local governments have authority to veto access on lo- cal routes over which they have jurisdiction. Local governments have independent authority both to define and implement access policies on routes over which they have jurisdiction. Other. Please explain. III. ENFORCEMENT A. What information is provided to the trucking industry regarding state access policies? Please check the items below which the state pro- vides and enclose copies of any written materials.
233 Maps showing access routes Lists of specific approved or restricted routes Special signs indicating approved or restricted routes Other. Please explain. Please estimate the frequency of citations issued by enforcement authorities to STAA vehicles which violate access policies by check- ing the appropriate box below. More than 10 citations per month 1 to 10 citations per month Less than 1 citation per month Does not apply (i.e. states without access restrictions) Would required marking of vehicle length and width on STAA vehi- cles for easy identification be of assistance in enforcing compliance with state access route restrictions? Yes ____ No Does your state have a special commercial enforcement unit of the state highway patrol that is in charge of truck compliance with state size and weight restrictions? Yes ____ No Do city or county law enforcement agencies enforce STAA vehicle access? Yes ____ No IV.. IMPACTS OF STAA VEHICLE OPERATION Has the state conducted an inventory (or partial inventory) of geo- metric improvements needed to accommodate the operation of STAA vehicles on existing or proposed access routes? If your answer is "No," please continue to Question B. If "Yes," please check the items below on which the state has information: Needed intersection upgrading . Needed lane and shoulder widening Other. Please specify. Has the state modified its geometric design practices for rehabilita- tion, reconstruction, or new construction projects to accommodate the operation of STAA vehicles on its roadways? ____ Yes ____ No
234 If your answer is "No," please go on to Question C. If "Yes," please describe what changes have been made. Has the state modified its traffic control operations on certain access routes to facilitate movement of STAA vehicles on these routes? Yes ______ No If your answer is "No," go on to Question D. If "Yes," please describe what changes have been made. Is the state's highway accident record system able to distinguish between STAA and non-STAA vehicles in reporting truck accidents? Yes ____ No If your answer is "No," go on to Question E. If "Yes," please provide annual reports or computer printouts showing truck accident in- volvements by vehicle type by road system starting with 1982. Has the state conducted any special studies on the access question? Please check those items below that apply and provide a copy of relevant reports or memos. Determining criteria for selecting specific access routes ap- propriate for STAA vehicle operation Impacts of STAA vehicles on access routes Other. Please describe V. SUMMARY OF MATERIALS REQUESTED (PLEASE CHECK THE FOLLOWING ITEMS THAT YOU ARE SENDING) Copy of regulations or laws specifying state access provisions Copy of application form used by trucking firms, terminals, ship- pers to apply for permission to use a certain access route Information provided to the trucking industry regarding state access policies, including maps or listing of access routes Reports or computer printouts of annual truck accident data by vehicle type and roadway system since 1982 or the most recent year available Special studies on access
235 SURVEY OF STATE TRUCKING ASSOCIATIONS ON TRUCK ACCESS STATE ASSOCIATION NAME SURVEY RESPONDENT WHO MAY BE CONTACTED FOR CLARIFICA- TION OF RESPONSES TO THIS QUESTIONNAIRE: NAME - ADDRESS TELEPHONE DEFINITIONS: 1. STAA Vehiclesâvehicles of the dimensions specified in the Surface Trans- portation Assistance Act (STAA) of 1982 as amended, which include: Twin trailer truck combinations using trailers of up to 28 feet long; Truck tractor-semitrailer combinations using semitrailers up to 48 feet long; Trucks with widths of up to 102 inches; Other specialized equipment as defined. The STAA of 1982 as amended further prohibited states from placing a length limit on truck-tractors used in STAA vehicle combinations and from limiting the overall length of STAA vehicles using the National Network (see definition below), and grandfathered longer semitrailers in those states which had accepted semitrailers in excess of 48 feet in length prior to December 1, 1982. 2. National or Designated Networkâthat network of Interstate, Federal-aid Primary, and other specified roads designated by the federal government subsequent to the STAA of 1982 for specific use by STAA vehicles. Access Routesâthose routes which provide access to and from the Na- tional Network to terminals and to facilities for food, fuel, repair, and rest. The 1982 STAA allowed the states to establish their own access policies. I. ACCESS PROVISIONS AND THEIR IMPLEMENTATION A. Briefly indicate your understanding of the state's method of providing reasonable access for those STAA vehicles authorized by the 1982
236 STAA from the National Network to terminals and to facilities by checking below those categories that apply. (More than one category may apply.) Unrestricted (i.e., all STAA vehicles can travel without regard to distance, lane width, or road type) Terminal Facilities Distance-based (e.g., x miles from the National Network) Terminal Facilities By specific route permit or signing of routes Terminal Facilities Combination of (a) and (b) (i.e., access is unrestricted for certain vehicle types, but distance-restricted for other vehicle types) Terminal Facilities Combination of (a) and (c) (i.e., access is unrestricted for certain vehicle types, but restricted by specific route permit or signing for other vehicle types) Terminal Facilities Combination of (b) and (c) (i.e., access is available by permit or signing beyond a general distance-based limit) Terminal ______ Facilities Other Terminal Facilities 1. How does the state define a terminal for the purpose of allowing access by STAA vehicles off the National Network? 2. What are the practical implications of this definition? If the state's access provisions require a route designation or special permit for STAA vehicle operation on specific routes, then please answer the following questions: 1. Who can apply for a permit? (e.g., trucking firms, shippers, termi- nals etc.) 2. What information must the applicant supply? (If there is a standard
237 application form, please enclose a copy.) I. Once a specific route is approved, either by a permit process or by signing the routes, who has authority to operate over this route? Please check the items below that apply. Only the party (and its contractors) who submitted the application All vehicles of the type allowed to operate over the route (e.g., all STAA twin trailer combinations) All STAA vehicles Other. Please explain NOTE: If the party who submitted the application is a terminal or shipper, what restrictions apply? For how long is the authority to operate an STAA vehicle over a specific route valid? Is there any charge for a permit or for route review? Yes ______ No If "Yes," please specify the amount for: First application or review Renewal Since the 1982 STAA went into effect, approximately what percent- age of applications have been approved by the state or local jurisdic- tions? _________ % What are the principal reasons for rejecting an application? - On average, how long does it take to process the application or review a route, including any local government reviews? D. Are local governments in the state involved in setting access policies? ____ Yes ____ No If your answer is "No," please skip to Question E. If "Yes," please answer the following questions: 1. Please specify the role of local governments by checking below the items which apply.
238 The state sets access policies and makes the final decision on access, but local governments have input by reviewing access requests on local routes over which they have juris- diction. Local governments have authority to veto access on local routes over which they have jurisdiction Local governments have independent authority both to define and implement access policies on routes over which they have jurisdiction Other. Please explain 2. What, if any, problems are created by local government involve- ment in setting truck access policies? Please explain. What information is provided to the trucking industry regarding state and local access policies? Please check the items below which the state provides and enclose copies of any written materials. Maps showing access routes Lists of specific approved or restricted routes Special signs indicating approved or restricted routes Other. Please explain Is the information provided adequate? ____ Yes ____ No. If your answer is "No," how could it be impro''ed? How would you rate state enforcement of access provisions? Please check the item below which most nearly applies.
239 Strict (i.e., enforcement authorities issue more than 10 cita- tions per month for access violations) Moderate (i.e., enforcement authorities issue between ito 10 citations per month for access violations). Lenient (i.e., enforcement authorities issue less than 1 citation per month for access violations) Other. Please explain H. What is the amount of the fine if a driver is caught driving illegally on an access route? ($) II. IMPACTS OF ACCESS POLICIES ON TRUCKING OPERATIONS Do trucking operators have difficulty accessing terminals, facilities for food, fuel, repair, or rest, or other points of loading and unloading because of access restrictions? Please check below, those items that apply. Difficulty accessing terminals Difficulty accessing facilities Difficulty accessing other points of loading and unloading If you have not checked any of the boxes above, please skip to Question I. If you have checked any of the boxes, please answer the following questions. What types of carriers are most adversely affected by access restric- tions? Please number in order of priority (e.g., 1 = most adversely affected and provide one or two examples of how access restrictions have affected the operation of these carriers). Private carrier For-hire truckload carrier For-hire less-than-truckload carrier Other. Please explain examples
240 What are the main access problems? Please number in order of priority (e.g., 1 = most. serious problem) Trucker cannot access his terminal Trucker cannot get to other points of loading and unloading Trucking operators cannot obtain permits in reasonable time period Driver, confusion over what are legal access routes Administrative burden of complying with access provisions (i.e., obtaining needed permits, route designations etc.) Other. Please explain Why is access a problem? Please check those items that apply. Trucker destination is not a terminal according to the state's definition of a terminal and thus access is not provided Trucker destination, whether a terminal or other point of loading, and unloading, is located too far from the National Network . Other. Please explain 'E. Where is access a problem? Please name specific routes, towns, areas of the state etc. F. Provide your worst case example of an access problem.
241 In what ways do you think state access provisions should be revised to ease the current restrictions? Has there been any movement or trend towards resolution of access problems in the state? ____ Yes ____ No If your answer is "Yes," please explain Has there been a history of negotiation between industry and state (and local governments if appropriate) regarding access restrictions and definitions of a terminal? ____ Yes ____ No If you answered "Yes," please explain
TABLE C-i THROUGH-TRAVEL MILEAGE ON THE FEDERAL-AID PRIMARY SYSTEM (Highway Statistics 1987 1988, 132, and TRB survey of state highway and transportation departments) National Additional Mileage Network State-Designated Percentage of All Open to STAA Percentage of All Region and State Mileage Mileage Primary Mileage Tractor-Semitrailers Primary Mileage East Alabama Connecticut Delaware District of Columbia Florida Georgia Kentucky Maine Maryland Massachusetts Mississippi New Hampshire New Jersey New York North Carolina Pennsylvania Rhode Island South Carolina Tennessee Vermont Virginia West Virginia Regional subtotal Midwest Arkansas 1,730 500 30 >2,500b >70 470 - 29 1,140 100 210 - 40 - 40 20 - 9 - 9 1,670 - 18 >5,000d >70 1,770 350 16 700k 25 2,690 - 51 - 51 380 - 16 1,9509 100 780 - 30 - 30 650 - 23 - 23 6,410 - 100 - 100 280 - 20 >900k >80 510 - 27 >1,000' >90 1,980 250' 26 - 26 3,210 - 60 - 60 2,120 >500' 19 - 19 90 - 19 380 100 1,930 - 29 - 29 2,590 - 36 - 36 350 - 24 - 24 2,590 10' 40 - 40 720 - 25 - 25 33,150 1,610 35 13,570 48 5,750 - S 100 - 100
Illinois 6,700 3,830k 92 - 92 Indiana 6,060 - 100 - 100 Iowa 7,680 >500k >80 - >80 Kansas 8,930 - 100 - 100 Louisiana 3,860 - 100 - 100 Michigan 5,470 960k 77 - 77 Minnesota 4,830 2,500k >80 - >80 Missouri 3,580 - 45 - 45 Nebraska 7,670 - 100 - 100 North Dakota 2,250 4,010' 100 - 100 Ohio 8,140 - 100 - 100 Oklahoma 6,240 - 100 - 100 South Dakota 6,470 - 100 - - 100 Texas 19,920 - 100 - 100 Wisconsin 3,720 2,500k 62 - 62 Regional subtotal 107,270 14,300 91 0 91 West Alaska 490 - 23 - 23 Arizona 2,510 >1,500'" >80 - >80 California 4,190 >5,000" >70 - >70 Colorado 5,240 - 100 - 100 Hawaii 540 - 100 - 100 Idaho 1,920 1,270° 100 - 100 Montana 6,540 - 100 - 100 Nevada 2,390 - 100 - 100 New Mexico 3,200 800" >80 - >80 Oregon 3,680 >500 >70 - >70 Utah 1,890 1,620'" 100 - 100 Washington 5,790 - 100 - 100 Wyoming 3,910 - 100 - 100 Regional subtotal 42,290 10,690 93 - 0 93 U.S. total 182,710 26,600 70 13,570 75 (continued)
TABLE C-i THROUGH-TRAVEL MILEAGE ON THE FEDERAL-AID PRIMARY SYSTEM (Highway Statistics 1987 1988, 132, and TRB survey of state highway and transportation departments) (continued) NOTE: Dashes = zero. Alabama has designated an additional 500-mi network for twins on which most STAA tractor-semitrailers are also allowed. bAjabama does not restrict 48-ft semitrailers; however, 102-in, vehicles are restricted to roads with 12-ft lanes. Mileage is estimated based on FAP mileage with 12-ft-wide lanes not already included on the National Network and state-designated networks. Semitrailers longer than 48 ft are confined to the National Network for through travel. Both 48-ft semitrailers and 102-in, vehicles are unrestricted. Mileage estimate is based on all FAP miles not already on the National Network. d102in vehicles are restricted to roads with 12-ft lanes. Mileage is estimated based on the number of FAP miles with 12-ft lanes not already on the National Network. Florida does not restrict 48-ft semitrailers. Georgia has designated an additional 350-mi network for twins, on which most STAA tractor-semitrailers are allowed. 102-in, trucks are allowed on all roads with 12-ft lanes. 'Additional miles on state-designated network open to 102-in, vehicles with overall lengths up to 67.5 ft. vehicles are unrestricted; vehicle wheelbase must not exceed 38 ft measured from the rear tractor axle to the rear trailer axle. Mileage estimate is based on number of FAP miles not already on the National Network. "New Hampshire does not restrict 48-ft semitrailers; however, 102-in, vehicles are restricted to roads with 12-ft lanes. Mileage estimate is based on number of FAP miles with 12-ft lanes not already on the National Network. 'New Jersey does not restrict 48-ft semitrailers. 102-in, vehicles are allowed on a 3,400-mi state-designated network that includes virtually all FAP miles. Mileage estimate is based on number of FAP miles not already on the National Network. 'Estimated FAP miles of access roads that connect on both ends to the National Network and are open to all vehicles. kStatedesignated truck network; maximum wheelbase and overall length restrictions may apply to some STAA vehicles. 'Restrictions apply to trucks that are longer than 75 ft. 'Virtually all FAP miles are open to STAA vehicles. "Most STAA vehicles are unrestricted. State network open to twins longer than 75 ft and tractor-semitrailers with wheelbases exceeding 40 ft, or an overall length exceeding 65 ft. °Wheelbase restrictions apply on some roads. "State network open to all STAA vehicles. "Addjtjonal state-designated highways open to all STAA vehicles, although overall length limit may apply.
TABLE C-2 ACCESS PROVISIONS FOR TWIN TRAILER TRUCKS (TRB survey of state highway and transportation departments) Percentage of Federal- Aid Primary Mileage Region and State Access Distance Limit Other Access Provisions Open to Twinst East Alabama 1 mi Additional 500-mi state-designated 30 network open to twins; 1-mi limit applies on National Network and state-designated network; special requests from local governments for access beyond 1-mi limit Connecticut 0.5 mi Special requests for access beyond 29 0.5-mi limit Delaware - Special requests for access 40 District of - Special requests for access 9 Columbia Florida' 1 mi on two-lane rural roads and on Special requests for access beyond 18 urban roads with 12-ft lanes; 3 mi distance limits on four-lane rural roads Georgian - Additional 350-mi state-designated 16 network open to twins; access provided on posted routes or by special request; access to services provided at posted interchanges Kentucky 5 mi - 51 Mainec 0.5 mi on four-lane urban roads; 2 Special requests for access beyond 16 mi on rural roads distance limits Maryland 1 mi to service facilities Shortest practical route to terminals 30
TABLE C-2 ACCESS PROVISIONS FOR TWIN TRAILER TRUCKS (TRB survey of state highway and transportation departments) (continued) Percentage of Federal- Aid Primary Mileage Region and State Access Distance Limit Other. Access Provisions Open to Twins" Massachusettsc Mississippi New Hamp- shirec New Jersey New Yorkc North Carolina Pennsylvaniac Rhode Island South Carolina Tennessee" Vermont Virginia West Virginia" 1 mi to service facilities 1,500 ft 3 mi 0.2 mi 1 mi on two-lane rural roads; 3 mi on four-lane rural roads; 1 mi on all urban roads 3 mi 0.5 mi 0.5 mi 0.5-2 mi Special requests for access Unlimited Special requests for access Special requests for access to terminals Special requests for access beyond distance limit Special requests for access beyond 3-mi limit Special requests for access beyond 0.2-mi limit Special requests for access beyond distance limits Special requests for access beyond 3-mi limit Shortest practical route 0.5-mi limit applies on posted Interstate interchanges only; special request for additional access Special requests for access beyond 0.5-mi limit 2-mi limit applies on National Network, although 96-in.-wide twins are also allowed on a 300-mi state-designated network with 0.5- mi access distance limit 23 100 20 27 26 60 19 19 29 36 24 40 25
100 92 Unlimited Additional 3,800-mi state-designated network open to twins; 5-mi limit applies on both National Network and state-designated network Unlimited Additional state-designated network (>500 mi) open to twins; 5-mi limit applies on Interstate highways only; however, access extends to all roads within the following distances of cities: City Population Distance (mi) Less than 2,500 3 2,500-25,000 4 25,000-100,000 6 100,000-250,000 8 More than 250,000 10 Unlimited Additional 1,000-mi state-designated network open to twins; 5-mi limit applies on both National Network and state-designated network Additional state-designated (>2,500- mi) network open to twins; special requests for additional access Unlimited Twins up to 75 ft in overall length are unrestricted; a 4,000-mi state- designated network with a 10-mi access distance limit is open to twins longer than 75 ft Midwest Arkansas - Ill inois" 5 mi Indiana - Iowa" 5 mi Kansas" - Louisiana 3 mi Michigan" 5 mi Minnesota" - Missouri 10 mi Nebraska - North Dakota - 100 >80 100 100 77 >80 45 100 100
TABLE C-2 ACCESS PROVISIONS FOR TWIN TRAILER TRUCKS (TRB survey of state highway and transportation departments) (continued) Percentage of Federal- Aid Primary Mileage Region and State Access Distance Limit Other Access Provisions Open to Twins" Ohio" - Unlimited 100 Oklahoma - Unlimited 100 South Dakota - Unlimited 100 Texas" - Unlimited 100 Wisconsin 5 mi Additional 2,500-mi state-designated 62 network open to twins; 5-mi limit applies on both National Network and state-designated network West Alaska 25 mi Special requests for access beyond 23 25-mi limit Arizona" - Twins are allowed on most routes >80 open to combination trucks, although an overall length limit of 65 ft applies on some highways California'" - Most twins are unrestricted; those 100 longer than 75 ft are restricted to the National Network and an extensive state-designated network; access to terminals and services is provided at posted interchanges with some additional restrictions colorado" - Unlimited 100 Hawaii - Unlimited 100
Idaho - Unlimited, although restrictions 100 apply on some highways for vehicles exceeding 75 ft in overall length Montana - Unlimited 100 Nevada - Unlimited 100 New Mexico 20 mi Additional 800-mi state-designated >70 network open to twins; 20-mi limit applies on National Network and state-designated network Oregond 0.5 mi Access distance limit applies on >70 National Network; additional access provided by 500-mi state- designated network; special requests from local governments for access from this network Utah - Unlimited. 100 Washington' - Unlimited 100 Wyoming" - Unlimited 100 NorE: Provisions in some states may have changed since the survey (June 1988). Dashes = no set limit. Access distance limit to both terminals and service facilities, unless otherwise specified. bPercentage of Federal-Aid primary miles on National Network and additional state-designated highways open to twins up to 75 ft in overall length (see Table C-i for more details). Access may be restricted subject to state definitions of terminal. "Access may be subject to local government regulation.
TABLE C-3 ACCESS PROVISIONS FOR STAA TRACTOR-SEMITRAILERS (TRB survey of state highway and transportation departments) Percentage of Federal- Aid Mileage Open to STAA Tractor- Region and State Access Distance Limit Other Access Provisions Semitrailersb East Alabamac - 96-in.-wide semitrailers up to 50 ft >70 long are unrestricted; 50-ft by 102- in. semitrailers are restricted to highways with 12-ft lanes; semi- trailers longer than 50 ft are re- stricted to the National Network and 1 mi for access; special re- quests from local governments for additional access Connecticut - Unlimited 100 Delaware - 96-in.-wide semitrailers up to 53-ft 40 long are unrestricted; 102-in, vehi- cles are granted access by special request District of - Special requests for access 9 Columbia Florida - 96-in.-wide by 48-ft semitrailers are >70 unrestricted; 102-in, vehicles are restricted to roads with 12-ft lanes; special requests for additional ac- cess
Georgiad - 48-ft by 102-in. semitrailers are al- 25 lowed on virtually all highways with 12-ft lanes, unless the overall length of the vehicle exceeds 60 ft; a 1,000-mi state-designated net- work is open to vehicles up to 67.5 ft long; access to terminals is pro- vided on posted routes or by spe- cial request; access to services is provided at posted interchanges Kentucky 5 mi - 51 Maine - 48-ft by 102-in. semitrailers must 100 conform to a 38-ft wheelbase limit (measured from the rear tractor axle to the center of the rearmost trailer axle or group of axles); oth- erwise, an access distance limit of 0.5 mi applies in urban areas and 2 mi in rural areas Maryland 1 mi to service facilities Shortest practical route 30 Massachusettsd - Special request.for access by 48-ft 23 semitrailers; 102-in, vehicles are al- lowed on all highways Mississippi - Unlimited 100 New Hamp- - 48-ft by 96-in.-wide semitrailers are >80 shire unrestricted; 102-in, vehicles are restricted to 12-ft lanes; special re- quests for additional access New Jersey 2 mi 48-ft by 96-in.-wide semitrailers are >90 unrestricted; a 4,000-mi state-des- ignated network is open to 102-in. vehicles; 2-mi limit applies on the National Network and state-desig- nated network
TABLE C-3 ACCESS PROVISIONS FOR STAA TRACTOR-SEMITRAILERS (TRB survey of state highway and transportation departments) (continued) - Percentage of Federal- Aid Mileage Open to STAA Tractor- Region and State Access Distance Limit° Other Access Provisions Semitrailers' New Yorkd 1,500 ft Special requests for access beyond 26 distance limit North Carolina 3 mi Special requests for access beyond 60 3-mi limit Pennsylvaniac 0.2 mi Special requests for access beyond 19 0.2-mi limit Rhode Island - Unlimited 100 South Carolina 3 mi Special request for access beyond 29 3-mi limit; 102-in, vehicles are al- lowed on all highways Tennesseec - Shortest practical route, subject to 36 state approval; semitrailers longer than 48 ft up to 53 ft are subject to a 41-ft wheelbase limit (meas- ured from the kingpin to the cen- ter of the rearmost trailer axle or group of axles) Vermont 0.5 mi 48-ft by 102-in. semitrailers are 24 allowed on most highways if overall length does not exceed 60 ft, otherwise 0.5-mi limit applies on posted Interstate interchanges; special requests for additional access
Virginia West Virginiac Midwest Arkansas IlljnOiSc Ui w Indiana lowac 0.5 mi Special requests for access beyond 0.5-mi limit 2 mi 48-ft by 96-in.-wide semitrailers are allowed on most highways, unless vehicle length exceeds 60 ft; 102- in. trucks and vehicles longer than 60 ft are restricted to the National Network plus 2 mi for access Unlimited 5 mi 5-mi limit applies on National Network and 3,800-mi state- designated network; a 40-ft wheelbase limit (measured from the kingpin to the center of the rearmost trailer axle) applies to all tractor-semitrailers Unlimited 5 mi Additional state-designated routes (>500 mi); 5-mi limit applies on Interstate highways only; however, access is extended to all roads within the following distances from cities: Population Distance (mi) Less than 2,500 3 2,500-25,000 4 25,000-100,000 6 100,000-250,000 8 More than 250,000 10 40 25 100 92 100 >80
TABLE C-3 ACCESS PROVISIONS FOR STAA TRACTOR-SEMITRAILERS (TRB survey of state highway and transportation departments) (continued) Percentage of Federal- Aid Mileage Open to STAA Tractor- Region and State Access Distance Limit Other Access Provisions Semitrailers" Kansas' - Unlimited 100 Louisiana 3 mi - 100 Michigan' 5 mi 5-mi limit applies on National 77 Network and 1,000-mi state- designated network; semitrailers over 50 ft long (up to 53 ft long) are subject to a 40.5-ft wheelbase limit (measured from the kingpin to the center of the rearmost trailer axle or group of axles) Minnesota' - 102-in, trucks are unrestricted; a 41- >80 ft wheelbase limit (measured from the kingpin to the center of the rearmost trailer axle) and an overall length limit of 65 ft apply on state-designated routes (>2,500 mi); special request for additional access Missouri 10 mi - 45 Nebraska - Unlimited 100 North Dakota - Unlimited 100 Ohio' - Unlimited 100 Oklahoma - Unlimited 100 South Dakota - Unlimited 100
Texasc Wisconsin West Alaska Arizonac California'' - Unlimited 5 mi 5-mi limit applies on National Network and 2,500-mi state- designated network; 102-in. vehicles are unrestricted; a 41-ft wheelbase limit (measured from the kingpin to the center of the rearmost trailer axle or group of axles) applies on all designated routes 100 62 25 mi Special requests for access beyond 23 25-mi limit - Semitrailers up to 102 in. wide and >80 65 ft in overall length are allowed on routes open to combination trucks; longer combinations must take shortest practical route between National Network and terminals - 102-in, vehicles and most semitrailers >70 up to 48 ft long are unrestricted; extensive state-designated network open to tractor-semitrailers longer than 65 ft with a wheelbase dimension exceeding 40 ft (measured from the kingpin to the center of the rearmost trailer axle); access to terminals and services provided on posted routes
TABLE C-3 ACCESS PROVISIONS FOR STAA TRACTOR-SEMITRAILERS (TRB survey of state highway and transportation departments) (continued) Region and State Access Distance Limit Other Access Provisions Percentage of Federal- Aid Mileage Open to STAA Tractor- Semitrailers" Coloradoc - Unlimited 100 Hawaii - Unlimited 100 Idaho - A 39-ft wheelbase limit (measured from the kingpin to the center of the rearmost trailer axle) applies on about 1,000 mi of highways; special requests on some mountain highways Montana - Unlimited 100 Nevada - Unlimited 100 New Mexico 20 mi 20-mi limit applies on National >80 Network and 800-mi state- designated network Oregonc 0.5 mi Access provided on 500-mi state- >70 designated network for 48-ft semitrailers (up to 65 ft in overall length); longer semitrailers (up to 53 ft) are restricted to the National Network plus 0.5 mi for access to terminals and services; special requests from local government for additional access Utah - Unlimited 100
Washington - Unlimited 100 Wyoming - Unlimited 100 Nore: Provisions in some states may have changed since survey (June 1988). Dashes = no set limit. Access distance limit to both terminals and service facilities, unless otherwise specified. bPercentage of Federal-Aid primary highway miles on National Network and state-designated routes effectively open to 48-ft by 102-in. semitrailers up to 65 ft in overall vehicle length (see Table C-i for more details). cAccess may be subject to local government regulations. dAccess may be restricted subject to state definitions of terminal.
APPENDIX D Carrier and Shipper Surveys INTERVIEW GUIDE FOR TRUCKLOAD FOR-HIRE CARRIERS TRUCK ACCESS STUDY NAME OF PERSON INTERVIEWED TITLE COMPANY DATE DEFINITIONS: 1. STAA Vehiclesâvehicles of the dimensions specified in the Surface Trans- portation Assistance Act (STAA) of 1982 as amended, which include: Twin trailer truck combinations using trailers of up to 28 feet long; Truck tractor-semitrailer combinations using semitrailers up to 48 feet long; Trucks with widths of up to 102 inches. Other specialized equipment as defined. The STAA of 1982 as amended further prohibited states from placing a length limit on truck-tractors used in STAA vehicle combinations and from limiting the overall length of STAA vehicles using the National Network (see definition below), and grandfathered longer semitrailers in those states which had accepted semitrailers in excess of 48 feet in length prior to December 1, 1982. 2. National or Designated Networkâthat network of Interstate, Federal-aid Primary, and other specified roads designated by the federal government subsequent to the STAA of 1982 for specific use by STAA vehicles. 3. Access Routesâthose routes which provide access to and from the Na- tional Network to terminals and to facilities for food, fuel, repair, and rest. The 1982 STAA allowed the states to establish their own access policies. 259
260 I. GENERAL INFORMATION ABOUT TRUCKING OPERATIONS A. Scale of Operations 1. Annual operating revenues for 1987 (or most recent year available) 2. Size of your truck fleet _______# tractors ______# trailers (total) van type # flatbed type ______# tank type # other 3. Operation of your truck fleet ______# of company-operated trailers ______# of trailers owned by or leased to owner-operators 4. Annual miles travelled in 1987 (or most recent year available) total truckload miles % full miles % empty miles NOTE: Ask for copy of most recent annual report B. Major commodities you handle______________________________ C. Are there any special characteristics of these commodities that af- fect your equipment requirements? Bulk (sizeâlbs. per cu.ft.) Weight Other (e.g., perishable commodities, special dimensions) D. Main areas of operation In how many states do you operate? (states) In what major regions are your trucking operations concentrated? % of Total Truckload Trips New England Mid-Atlantic Southeast South Central Midwest West TOTAL 100%
261 E. General characteristics of truck trips Total number of truckload trips in 1987 (or most recent year avail- able) # Average length of truckload trip (miles) Average number of unloading points per truckload trip # II. USE OF STAA VEHICLES A. What percent of your trailers are STAA dimensions? _________ % B. What percent of your truckload trips are made by STAA vehi- cles?_% overall ____% by STAA twins ______% by STAA semis (48 ft & longer grandfathered lengths) ______% by other STAA (e.g., 96" wide but STAA length) C. What dimension vehicles do STAA trucks replace? D. If you use 102"-wide trailers, what percentage of these trailers have 102"-wide axles?_% E. If you use STAA semis, what is the kingpin-to-centerpoint of rear axle setting ft. and what is the length of the wheel- base of the tractors you use ___________ in.? Why do you use this kingpin setting? Would you have any problem with a 41 ft kingpin setting? Please explain. F. What are the benefits of using STAA vehicles?_________________ NOTE: Ask this as an open-ended question and then ask the respon- dent to rank his answers in order of importance Provide more capacity ______Can load the vehicles more efficiently and safely (e.g., better weight distribution etc.) Shippers request vehicles of STAA dimensions ______Other
G. What are or would be the relative advantages and disadvantages of using twins for your operations? (ask only if they use semis) H. What are or would be the relative advantages and disadvantages of using semis for your operations? (ask only if they use twins)_ I. General characteristics of STAA truckload trips Type of commodities hauled Does your typical STAA load weigh out or cube out?________ Average density per load lbs/cu. ft Average weight per load lbs/load Average distance per truckload trip (miles) Average number of unloading points per truckload trip # J. Characteristics of points of loading and unloading Types Loading Points Unloading Points % mfgr.operation % mfgr. operation % wrhse/whol. distr. ______% wrhse/whol.distr. ctr ctr % retail operation % retail operation % other_______ % job site % other______ Location Loading Points Unloading Points % Rural ______% Rural % Suburban ______% Suburban % Urban (i.e., in ______% Urban (i.e., in cities) cities) a. If access to points of loading or unloading were restricted to within 1 to 2 road miles of Interstate highways or other major primary routes designated as part of the National Network, approximately what percentage of your points of loading and 262
263 unloading would be located within this mileage restriction? If this access restriction were relaxed to 5 road miles from the National Network, then what percentage of your points of loading and unloading would be located within this mileage restriction?_% If this access restriction were relaxed to 10 road miles from the National Network, then what percentage of your points of loading and unloading would be located within this mileage restriction?_% K. Relationship with shippers Do you have long-term contracts with your shippers? __Yes No Do they require you to use certain kinds of equipment, such as STAA trailers? Yes ____No What percent of your trips using STAA equipment are on regular routes?_% L. What are your estimated costs per mile (i.e., including labor, fuel, maintenance, and depreciation) using: STAA vehicles ___________________________________ cents/mile Non-STAA vehicles _____________________________ cents/mile M. Projected use of STAA vehicles What percent of your trips will be made by STAA vehicles in 5 years? (percent) Do you anticipate any change in the composition of your STAA fleet? N. Are financial constraints preventing you from purchasing STAA equipment? 0. Do you provide any special driver training in the use of STAA vehicles? Yes No P. Do you keep records on the number of accidents and mileage traveled by STAA vehicles relative to non-STAA vehicles (if any) in your fleet? Yes No Follow-up if answer is "Yes" [i.e., see if they can send annual accident data by truck type and travel (exposure) data for these same vehicle types].
264 III. IMPACTS OF STAA TRUCK ACCESS RESTRICTIONS What percent of your truckload trips, if any, would you estimate are adversely affected by policies of state and local governments restricting access to points of loading and unloading? % Cannot get from or to required destination using STAA equipment and so must use non-STAA equipment Can get from or to destination, but must make lengthy detours Cannot obtain permit for trip in reasonable time period % No problem with access NOTE: Ask for examples of each type of access problem Are there any particular regions of the country where you do business that have greater problems with access than others? If so, please specify those regions (or states) Are all of your points of loading and unloading considered termi- nals for the purpose of access in all states in which you operate? ____Yes ____No If the answer is "No," please list those states in which the definition of terminals restricts access to required points of loading and unload- 1. Have local government policies presented a problem in pro- viding adequate access to points of loading and unloading? Serious problems Moderate problems Little or no problems Please give examples of problems 2. Would a "one-stop" procss at the state level for coordinating local government review of access route requests be desirable?
265 Ask for specific examples of where carrier has had to apply for an access permit, obtain a route designation, or negotiate with a state or local government to obtain access to points of loading or unloading where the process has worked? where it has not worked? Example of process working Example of process not working Can you identify the costs of restrictive access provisions? NOTE: Ask this as an open-ended question and then ask the respon- dent to rank his answers in order of importance. Try to obtain specific examples with cost estimates and then ask how representative these costs are of the entire operation. Additional equipment (i.e., two fleetsâone STAA and one non-STAA) Additional time to reach points of loading and unloading resulting in additional line-haul costs Additional administrative and compliance costs (obtaining access permits, apprising drivers of legal routes etc.) Other Provide your worst case example of an access problem and its costs
266 In your opinion, what information should states provide to the trucking industry, and in what form, concerning their access poli- cies?________________________________________ In what ways do you think truck access provisions should be re- vised to ease the à urrent restrictions?___________________ If these changes were made, what percentage of your trips would be made using STAA vehicles? % What would be the main effect on your trucking operations from a relaxation of current access restrictions?______________________ INTERVIEW GUIDE FOR LESS-THAN-TRUCKLOAD FOR-HIRE CARRIERS TRUCK ACCESS STUDY NAME OF PERSON INTERVIEWED___________________ TITLE COMPANY DATE DEFINITIONS: 1. STAA Vehiclesâvehicles of the dimensions specified in the Surface Trans- portation Assistance Act (STAA) of 1982 as amended, which include: Twin trailer truck combinations using trailers of up to 28 feet long; Truck tractor-semitrailer combinations using semitrailers up to 48 feet long; - Trucks with widths of up to 102 inches. Other specialized equipment as defined. - The STAA of 1982 as amended further prohibited states from placing a length limit on truck-tractors used in STAA vehicle combinations and from limiting the overall length of STAA vehicles using the National
267 Network (see definition below), and grandfathered longer semitrailers in those states which had accepted semitrailers in excess of 48 feet in length prior to December 1, 1982. National or Designated Networkâthat network of Interstate, Federal-aid Primary, and other specified roads designated by the federal government subsequent tothe STAA of 1982 for specific use by STAA vehicles. Access Routesâthose routes which provide access to and from the Na- tional Network to terminals and to facilities for food, fuel, repair, and rest. The 1982 STAA allowed the states to establish their own access policies. I. GENERAL INFORMATION ABOUT TRUCKING OPERATIONS A. Scale of Operations 1. Annual operating revenues for 1987 (or most recent year available) 2. Size of your truck fleet _______# tractors ______# trailers (total) 3. Annual miles travelled in 1987 (or most recent year available) _______total line-haul miles (terminal-to-terminal) % full miles % empty miles ______total pick-up and delivery miles NOTE: Ask for copy of most recent annual report B. Main areas of operation In how many states do you operate? (states) Total number and distribution of your terminals facilities by region Terminals and Breakbulk Facilities (%) New England Mid-Atlantic Southeast South Central Midwest West TOTAL 100 Percent C: General characteristics of truck trips Total number of line-haul trips (i.e., terminal-to-terminal) in 1987 or most recent year available (#) Average length of trip (miles)
268 II. USE OF STAA VEHICLES A. What percent of your trailers are STAA dimensions? _________ % B. What percent of your line-haul trips are made by STAA vehicles? % overall % by STAA twins % by STAA semis (48 ft & longer grandfathered lengths) % by other STAA (e.g., 96" wide but STAA length) C. If you use 102"-wide trailers, what percentage of these trailers have 102"-wide axles? (%) D. What dimension vehicles do these STAA trailers replace? E. Do you use twin pups for local pick-up and delivery? F. General characteristics of STAA line-haul trips T'pe of commodities hauled Average density of line-haul load (lbs./cu.ft.) Average distance per line-haul trip (miles) G. 1. If terminal access were restricted to within 1 to 2 road miles of Interstate highways or other major primary routes designated as part of the National truck Network, approximately what percentage of your terminals would be located within this mile- age restriction? % If this access restriction were relaxed to 5 road miles from the National Network, then what percentage of your terminals would be located within this mileage restriction? ________________ % If this access restriction were relaxed to 10 road miles from the, National Network, then what percentage of your terminals would be located within this mileage restriction?._______________ % H. What are the benefits of using STAA vehicles?_________________ NOTE: Ask this as an open-ended question and then ask the respon- dent to rank his answers in order of importance Provide more cubic capacity per line-haul trip
269 Reduce rehandling of shipments at terminals (i.e., breakbulk on pups) Provide greater operating flexibility (e.g., use of pups for local delivery etc.) ______Other I. What are your estimated savings from using STAA vehicles? Try to estimate on a per trip basis Percent reduction in total number of line-haul trips because of greater capacity of STAA vehicles______ % reduction NOTE: try to find out equivalency between STAA and non-STAA line-haul trips (i.e., 1 non-STAA vehicle trip = 0._? STAA vehicle trip and then the percentage of all line-haul trips where this substitution effect occurs) ______STAA vehicle line-haul costs (i.e., including labor, fuel, main- tenence, and depreciation) per mile_cents/mile non-STAA vehicle line-haul costs (i.e., including labor, fuel, maintenance, and depreciation) per mile_cents/mile Number of shipment rehandlings per trip using STAA vehi- cles_# per trip Number of shipment rehandlings per trip using non-STAA vehicles_# per trip ____Costs of shipment rehandling per trip $ per trip _______Other savings $ per trip Projected use of STAA vehicles What percent of your trips will be made by STAA vehicles in 5 years? (percent) Do you anticipate any change in the composition of your STAA fleet? K: Are financial constraints preventing you from purchasing STAA equipment? Do you provide any special driver training in the use of STAA vehicles? Yes No Do you keep records on the number of accidents and mileage traveled by STAA vehicles relative to non-STAA vehicles (if any) in your fleet?_Yes_No
270 Follow-up if answer is "Yes" [i.e., see if they can send annual accident data by truck type and travel (exposure) data for these same vehicle types]. III. IMPACTS OF STAA TRUCK ACCESS RESTRICTIONS What percent of your line-haul trips, if any, would you estimate are adversely affected by policies of state and local governments restricting access to your terminals? Cannot get to your terminals using STAA equipment and so must use non-STAA equipment % Can get to your terminals with STAA equipment, but must make lengthy detours % No problem with access NOTE: Ask for examples of each type of access problem Have you experienced any difficulty using twin pups for local pick-up and delivery? Yes No If "yes," what percentage of your local trips are affected? - % NOTE: Ask for examples 1. Have local government policies presented a problem in pro- viding adequate access to company terminals or delivery points? Serious problems Moderate problems Little or no problems Please give examples of problems
271 2. Would a "one-stop" process at the State level for coordinating local government review of access route requests be desirable? Are there any particular regions of the country where you do business that have greater problems with access than others? If so, please specify those regions (or states) Could you give an example of where the company has had to ap- ply for an access permit, obtain a route designation, or negotiate with a state or local government to obtain terminal access where the process has worked? where it has not worked? Example of process working Example of process not working Can you identify the costs of restrictive access provisions? NOTE: Ask this as an open-ended question and then ask the respon- dent to rank his answers in order of importance. Try to obtain specific examples with cost estimates and then ask how representative these costs are of the entire operation. Additional equipment (i.e., two fleetsâone STAA and one non-STAA) Additional costs of rehandling shipments at terminals Additional time to reach destinations resulting in additional line-haul costs Additional administrative and compliance costs (obtaining access permits, apprising drivers of legal routes etc.) ______Other
272 Provide your worst case example of an access problem and its costs In your opinion, what information should states provide to the trucking industry, and in what form, concerning their access poli- cies? In what ways do you think truck access provisions should be re- vised to ease the current restrictions?_____________________________ If these changes were made, what percentage of your trips would be made using STAA vehicles? _________________________ % What would be the main effect on your trucking operations from a relaxation of current access restrictions?________________________ INTERVIEW GUIDE FOR SHIPPERS/PRIVATE CARRIERS TRUCK ACCESS STUDY NAME OF PERSON INTERVIEWED____________________ TITLE COMPANY DATE DEFINITIONS: 1. STAA Vehiclesâvehicles of the dimensions specified in the Surface Trans- portation Assistance Act (STAA) of 1982 as amended, which include:
273 Twin trailer truck combinations using trailers of up to 28 feet long; Truck tractor-semitrailer combinations using semitrailers up to 48 feet long; Trucks with widths of up to 102 inches. Other specialized equipment as defined. The STAA of 1982 as amended further prohibited states from placing a length limit on truck-tractors used in STAA vehicle combinations and from limiting the overall length of STAA vehicles using the National Network (see definition below), and grandfathered longer semitrailers in those states which had accepted semitrailers in excess of 48 feet in length prior to December 1, 1982. National or Designated Networkâthat network of Interstate, Federal-aid Primary, and other specified roads designated by the federal government subsequent to the STAA of 1982 for specific use by STAA vehicles. Access Routesâthose routes which provide access to and from the Na- tional Network to terminals and to facilities for food, fuel, repair, and rest. The 1982 STAA allowed the states to establish their own access policies. I. GENERAL INFORMATION ABOUT TRUCKING OPERATIONS A. Scale of Operations Main line of Business Annual operating revenues for 1987 (or most recent year available) NOTE: Ask for copy of most recent annual report B. Major commodities you C. Percent of shipments (i.e., either volume or #) that are moved by truck % D. What type of truck services do you use? _______Own fleet (i.e., private carrier) For-hire ______Combination: ______% Private ______% For-hire E. What is the size of your truck fleet (private and contract for-hire)? _______# of tractors ______# of trailers (total) # van type # flatbed type # tank type ______# other
274 Annual miles travelled in 1987 (or most recent year available) total truckload miles full miles empty miles For shippers contracting with for-hire carriers, ask the following questions about .the shipper's relationship. with their carriers: Do you have long-term contracts with your carriers? Yes ____No Do you require your carriers to have dedicated fleets for exclusive carriage of your shipments? Yes ____No Do you require your carriers to use certain types of equipment, such as STAA trailers? _Yes ____No If the answer is "Yes," ask for a more detailed explanation H. Are there any special characteristics of your commodities that af- fect your shipping requirements? Bulk (sizeâlbs. per cu.ft.) Weight Other (e.g., perishable commodities, special dimensions) I. Main areas of operation In how many states do you make truck shipments? (states) In what major regions are your truck shipments concentrated? % of Shipments New England Mid-Atlantic Southeast South Central Midwest .⢠West TOTAL 100% J. General characteristics of truck shipments 1. Total number of truck shipments in 1987 (or most recent year available)
275 Average distance per truck shipment (i.e., average length oftruck shipment) (miles) Average number of unloading points per truck shipment II. USE OF STAA VEHICLES A. What percent of the trailers you use are.STAA dimensions? - % B. What percent of your truck shipments are moved by STAA vehi- cles?_% overall ______% by STAA twins ______% by STAA semis (48 ft & longer grandfathered lengths) ______% by other STAA (e.g., 96" wide but STAA length) C. What dimension vehicles do these STAA trucks replace? D. If you use 102"-wide trailers, what percentage of these trailers have 102"-wide axles?_% E. If you use STAA semis, what is the kingpin-to-centerpoint of rear axle setting ft. and what is the length of the wheelbase of the tractor you use_in.? Why do you use this kingpin setting? Would you have any problem with a 41 ft kingpin setting? Please explain. F. What are the benefits of using STAA vehicles?, NOTE: Ask this as an open-ended question and then ask the respon- dent to rank his answers in order .of importance Provide more capacity Provide greater operating flexibility (i.e., can handle more deliveries per shipment) ______Can load the vehicles more efficiently and safely'(e.g., better weight distribution etc.) ______Other
What are or would be the relative advantages and disadvantages of using twins for your operations? (ask only if they use semis) What are or would be the relative advantages and disadvantages of using semis for your operations? (ask only if they use twins) General characteristics of STAA vehicle trips Type of commodities shipped Does your typical STAA load weigh out or cube out?________ Average density per load __________________________ lbs/cu. ft Average weight per load __________________________ lbs/load Average distance per truck shipment (miles) Average number of unloading points per truck shipment - # Characteristics of your receivers 1. Types % manufacturing operation % warehouse/wholesale distribution center % job site % retail operation % other___________________________ Location % Rural % Suburban % Urban (i.e., in cities) If access to points of loading or unloading were restricted to within 1 to 2 miles of Interstate highways or other major pri- mary routes designated as part of the National truck Network, approximately what percentage of your points of loading and unloading would be located within this mileage restriction? If this access restriction were relaxed to 5 miles from the Na- tional Network, then what percentage of your points of loading and unloading would be located within this mileage restriction? ____% 276
277 c. If this access restriction were relaxed to 10 miles from the National Network, then what percentage of your points of loading and unloading would be located within this mileage restriction?_% K. What are your estimated savings from using STAA vehicles? Try to estimate on a per shipment basis ______% reduction in total number of shipments because of greater capacity of STAA vehicles_% reduction NOTE: try to find out equivalency between STAA and non-STAA shipments (i.e., 1 non-STAA shipment = 0._? STAA ship- ment) and then the percentage of shipments where this substitution effect occurs Fstimated shipment costs per mile (including labor, fuel, maintenance and depreciation) using STAA equipment ____________ cents/mile Fstimated shipment costs per mile using non-STAA equip- ment ___________ cents/mile Savings from loading efficiencies savings/shipment ______Other estimated savings (e.g., administrative costs, ware- housing costs) savings/shipment L. Projected use of STAA vehicles What percent of your shipments will be made by STAA vehicles in 5 years? (percent) Do you anticipate any change in the composition of your STAA fleet? M. Questions for shippers who have private fleets or mixed fleets only: Do you provide any special driver training in the use of STAA vehicles? Yes No Do you keep records on the number of accidents and mileage travelled by STAA vehicles relative to non-STAA vehicles (if any) in your fleet?_Yes ______No Follow-up if answer is "Yes" [i.e., see if they can send annual accident data by truck type and travel (exposure) data for these same vehicle types]. III. IMPACTS OF STAA TRUCK ACCESS RESTRICTIONS A. What percent of your shipments, if any, would you estimate are adversely affected by policies of state and local governments re- stricting access to points of loading and unloading?
% Cannot get from or to required destination using STAA equipment and so must use non-STAA equipment % Can get from or to destination, but must make lengthy detours % No problem with access NOTE: Ask for examples of each type of access problem Are there any particular regions of the country where you do business that have greater problems with access than others? If so, please specify those regions (or states) Are all of your points of loading and unloading considered ter- minals for the purpose of access in all states in which you ship? Yes ____No If the answer is "No," please list those states in which the definition of terminals restricts access to required points of loading and unload- ing 1. Have local government policies presented a problem in pro- viding adequate access to points of loading and unloading? Serious problems Moderate problems Little or no problems Please give examples of problems 2. Would a "one-stop" process at the state level for coordinating local government review of access route requests be desirable? Have you applied for an access permit, obtained a route designa- tion, or negotiated directly with a state or local government to obtain access to points of required loading and unloading? Yes ____No If the answer is "Yes," provide examples of where the process has worked and where it has not worked 278
279 Example of process working Example of process not working Can you identify the costs of restrictive access provisions? (Try to obtain specific examples with cost estimates and then ask how representative these costs are of the entire operation) Additional equipment (i.e., two fleetsâone STAA and one non-STAA) Additional time to reach points of loading and unloading resulting in additional shipment costs Additional administrative and compliance costs (obtaining access permits, apprising drivers of legal routes etc.) ______Other_________________________________________ Provide your worst case example of an access problem and its costs In your opinion, what information should states provide to the trucking industry, and in what form, concerning their access poli- cies?
In what ways do you think truck access provisions should be re- vised to ease the current restrictions? If these changes were made, what percentage of your shipments would be made using STAA vehicles?_% What would be the main effect on your shipping operations from a relaxation of current access restrictions?________________________ 280
APPENDIX E Off tracking One of the key issues in determining appropriate highways for access is the extent to which existing highways, particularly those with restrictive geometry, can safely accommodate STAA vehicles. Of particular concern is the maneuverability of the STAA vehicles relative to each other, to the vehicles they replace, and to the design vehicles for which existing high- ways were constructed. Poor vehicle maneuverability affects both highway safety and roadway maintenance costs. First, vehicles with poor maneuverability may not be able to stay within their lanes and may intrude into adjacent or oncoming traffic lanes, thereby increasing accident risk. Second, vehicles with poor maneuverability may encroach on highway shoulders, causing structural damage, or strike curbs and roadside appurtenances, increasing mainte- nance and repair bills. In this appendix The major factors that affect vehicle maneuverability are identified and The operating performance of the most common STAA vehicle configurations is compared with that of benchmark vehicles on roads with various geometric characteristics. OFFTRACKING The maneuverability of a vehicle on a highway is most commonly assessed by examining vehicle offtracking. Offtracking is defined as the difference in the paths of the front and rear wheels of a vehicle as it negotiates a turn (Fambro et al. 1988, 2-3). Although offtracking is a phenomenon com- mon to all vehicles, it is more pronounced for trucks, particularly trucks 281
282 with long wheelbases. From the perspective of highway design, the rele- vant measure of offtracking is the swept path width, which is the amount of roadway width the vehicle takes up in negotiating the turn (i.e., the amount of offtracking plus the width of the vehicle).' If the swept path width is greater than the lane width, the vehicle must encroach on another lane or the highway shoulder to negotiate the turn. Off tracking is most pronounced at low speeds when the rear wheels of a vehicle track inward of the front wheels. At high speeds, the opposite effect can occur; the lateral acceleration of the vehicle as it negotiates a curve creates a dynamic effect that causes the rear wheels to track outward from the front wheels, which could more than offset the effects of inward offtracking (personal communication with W. D. Glauz and D. W. Harwood, Midwest Research Institute, January 26, 1989).2 How- ever, high-speed or negative offtracking is quite small, typically no greater than about 1.4 ft (TRB 1986, 271, 272), at which point vehicle rollover becomes the greater concern.3 Although thereis no absolute line of demarcation between low-speed and high-speed offtracking, AASHTO policies on geometric design sug- gest that, at approximately 40 mph on curves with radii greater than 400 ft, the differences in the offtracking behavior of many large trucks are insignificant (AASHTO 1984, 238). Thus low-speed offtracking is princi- pally a problem at intersections and sharp curves on roads on which vehicle operating speeds are generally less than 40 mph, conditions that may be prevalent on many access roads. High-speed offtracking is likely to be a problem on roads with curves on which speeds may substantially exceed 40 mph and on interchanges and ramps. The problem created by offtracking is differences between the space demands of a vehicle and the space that has been provided in the geomet- ric design of the roadway (Ervin and Guy 1986, 252). The extent of this problem is a function of both vehicle and roadway characteristics. The amount a vehicle offtracks at low speeds depends on the length of the tractor and trailer wheelbases, particularly the latter, and the number of articulation points (AASHTO 1984, 238). All else being equal, the lOnger the wheelbases and the fewer the articulation points, the greater the offtracking (Guide for Monitoring and Enhancing Safety on the National Truck Network 1986, 10). Thus the STAA tractor-semitrailer is the critical vehicle with respect to low-speed offtracking. Vehicle offtracking at low speeds is also a function of roadway geome- try. All else being equal, the shorter the turning radius at intersections and the sharper the curves on highways, the greater the offtracking. Restrictive geometric conditions are likely to be more prevalent on access routes, most of which were not built to the same standards as the highways on the National Network. Fortunately, at locations where offtracking is
283 most severe (intersections built to lower design standards) trucks are traveling at slow speeds, so the accident consequences are less critical. MEASURING OFFTRACKING Mathematical formulas for estimating truck offtracking were developed by the Society of Automotive Engineers and the Western Highway Insti- tute in the 1960s. These formulas allow highway engineers to calculate the maximum expected offtracking for a particular vehicle for a curve of a given radius; however, they are limited because they show neither the shape of the vehicle path, and thus the amount of offtracking at any particular point, nor the location at which the maximum offtracking occurs, nor if this maximum value will actually be reached for a specific curve (Fong and Chenu 1986, 7). The last point is particularly important because the maximum offtracking calculated by the formulas may over- state actual offtracking in situations in which the vehicle pulls out of the turn before maximum offtracking occurs (Fong and Chenu 1986, 7). UMTRlICaltrans Offtracking Computer Model Computer programs that can provide more precise measurement of low- speed offtracking are now available. The California Department of Trans- portation (Caltrans) has modified and extended an offtracking computer model developed by the University of Michigan Transportation Research Institute (UMTRI) for the Federal Highway Administration that is widely available for personal computer use. (The Caltrans model runs on a mainframe.)4 Both models require the following input: (a) roadway char- acteristics, including the degree and radius of the curve, and (b) vehicle characteristics, including the trailer wheelbase measured from the king- pin to the center of the rear axle or axles, the tractor wheelbase, and the fifth wheel offset (Figures E-1 and E-2). The distance from the kingpin to the center of the rear axle or axles is the vehicle characteristic that has the greatest effect on the extent of offtracking. Offtracking Calculations for STAA Vehicles The UMTRI/Caltrans computer model was used to provide special com- puter tabulations for this study. The study committee identified eight design vehicles for analysis, including two baseline vehicles of pre-STAA dimensionsâone with a 37-ft trailer, the WB-50 or the design vehicle for
BE of of le FIGURE E-1 Offtracking computer model inputs, roadway characteristics: turn angle and turn radius. Kingpin 5th Wheel Offset Tractor Wheelbase I I I Kingpin to Center of Rear Axle or Axles FIGURE E-2 Offtracking computer model inputs, vehicle characteristics: tractor wheelbase, 5th wheel offset, kingpin to center of rear axle (most important).
TABLE E-1 DESIGN VEHICLE DIMENSIONS FOR OFFTRACKING COMPUTER MODEL ANALYSIS Vehicle Dimension (ft) Configuration A B C D E F G H T 37-ft semitrailer, conventional cab 3 18 0 30.0 4.0 - - - 55 (WB-50) 45-ft semitrailer, conventional cab 3 18 0 37.5 4.5 - - - 63 STAA twin trailer, cab over engine 3 10 0 22.5 2.5 6 22.5 2.5 69 STAA twin trailer, conventional cab 3 13 0 22.5 2.5 6 22.5 2.5 72 48-ft semitrailer, conventional cab 3 18 0 40.5 4.5 - - - 66 48-ft semitrailer, California cab 3 20 0 40.5 4.5 - - - 68 53-ft semitrailer, conventional cab 3 18 0 45.5 4.5 - - - 71 59-ft semitrailer, conventional cab 3 18 0 51.5 4.5 - - - 77 KEY: A = Front overhang B = Tractor wheelbase length C = Fifth wheel offset D = First trailer wheelbase length E = First trailer rear overhang F = Distance from rear trailer axle to hitch point of second trailer G = Second trailer wheelbase length H = Second trailer rear overhang T = Total vehicle length Dash = Not applicable C C # A - H B D E- F - G
286 many existing intersections, and the second with a 45-ft trailerâtwo STAA twin trailer trucks, and four STAA tractor-semitrailers of trailer lengths ranging from 48 to 59 ft (Table E-1). Note that the rear axles of a trailer can often be moved fore and aft. The dimensions given in Table E-1 (i.e., Dimension D) are for the farthest aft positions. The output produced by the Caltrans model is shown in Figure E-3 for a 90-degree intersection turn with a turn radius of 60 ft. The output in- cludes, among other items, the amount of offtracking at the beginning and the end of a curve, the maximum offtracking value and its location, and a graphic display of the amount and location of the offtracking and the swept path width as the truck moves along the curve (Fong and Chenu 1986, 9). For an intersection with these geometrics, each foot of semi- trailer length measured from the kingpin to the center of the rear axle or axles adds approximately three-fifths of a foot of offtracking, if all other vehicle dimensions are held constant. Sensitivity analyses performed by Caltrans showed that varying the other vehicle dimensions has only a minor effect on offtracking. For example, for every 1-ft increase in tractor wheelbase length, offtracking increases by only 0.23 ft. The placement of the kingpin relative to the rear tractor axle or axles (i.e., the fifth wheel offset) makes little practical difference in the amount of offtracking (Fong and Chenu 1986, 29-31); maximum offtracking occurs when the kingpin is located directly over the center of the rear tractor axle or axles. This is the assumption used in the computer offtracking tabulations for this study. Figures E-4 through E-11 provide graphic representations of the maxi- mum offtracking for each of the design vehicles, assuming that the rear trailer axles are in the farthest back position, for a range of geometric conditions.5 These graphs can be usedto determine the pavement width required for a particular vehicle to negotiate a turn or curve. For example, to compare the pavement width required for the 48-ft STAA tractor- semitrailer with a conventional cab (Figure E-8) with that required for the WB-50 (Figure E-4) to negotiate a 60-degree curve with a 200-ft turn radius, read along the y-axis until the 60-degree turn is reached; then run a horizontal line until it intersects with the TR = 60-ft curve; then move in a vertical line down to the x-axis to read the amount of offtracking. The amount is about 3.2 ft for the WB-50 and about 5 ft for the 48-ft tractor- semitrailer. Next, add the amount of offtracking to the vehicle width, or 7.58 ft (one-half of the 8.5-ft trailer width plus one-half of the smaller 6.66-ft width of the tractor steering axle)6 to find the swept path, or pavement width needed to negotiate the turn. The WB-50 requires ap- proximately 11ft of pavement, and the longer-wheelbase 48-ft tractor-
BC - -------------------------------- KEY BC = Beginning of Curve MOT =MaxirnurnOffiracking EC End of Curve \MOT TRUCK OFFTRACKING \ Tractor-Semitrailer with Tractor A GEOM Y Wheelbase Length 0120 ft. Trailer Wheelbase Length 0138 ft. and Fifth Wheel Offset of 0 ft. Turn = 90.00 Degrees Radius = 60.00 Feet Offset = 3.33 Feet (with a radius of 66.67 Feet to C'l of Front Axle) SIMULATION PARAMETER: Distance Travelled After Reaching End of Curve = 140.00 Feet Distance Increment for Simulation Calculations = 1.00 Feet VEHICLE CONFIGURATION: Vehicle Wheelbase Distance That 5th Wheel (or Hitch) Label Unit # Length Lies in Front of the Rear Axle 1 20.00 0.00 Tractor 2 38.00 0.00 Semitrailer ADDITIONAL VEHICLE REFERENCE POINTS: Vehicle Distance in Distance Right Label Unit # Front of Rear Axle (or Left) of C'line 1 20.00 -3.33 Lt Frnt Steer Tire 2 0.00 4.25 Rt Rear Semi Bogie OFFTRACKING SUMMARY: Location Amount of (Degree) Offtracking 0.00 5.43 (BC 61.27 14.38 (MOT) 90.00 11.32 ( EC EC FIGURE E-3 Example of offtracking computer model output for a 90-degree turn with a 60-ft turning radius (Caltrans).
180 150 - - I 0o 0 0 - u 0 ) 0 0 ( 0 cJ c'J ,- CO - II II II II II II II I, cc cc cc cc cc cc I- - TR = Turn Radius (ft) 30 -'I '45 6 7 8 9 10 11 12 13 14 15 16 17 MAXIMUM OFFTRACKING (feet) FIGURE E-4 Maximum offtracking for 37-ft tractor-semitrailer (WB-50) on turns of varying geometry (Caltrans).
180 150 120 H H CO R=TurnRadius(ft) 30 0 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 MAXIMUM OFFTRACKING (feet) FIGURE E-5 Maximum offtracking for 45-ft tractor-semitrailer on turns of varying geometry (Caltrans).
1 150 120 0 it) 0 10 0 0 o c Cli C\I 1 CO II II H II II H gg cc I-I- I- I- I- I.- IF I'.. TR I I Turn Radius (ft) 60 30 3 4 5 6 7 8 9 10 Ii 12 13 14 15 16 17 MAXIMUM OFFTRACKING (feet) FIGURE E-6 Maximum offtracking for STAA twin trailer truck (cab over engine) on turns of varying geometry (Caltrans).
180 150 120 V Ui -J c 90 z z - I- 60 30 C o ol 01 Cl) Câ¢.J C'i .- (I OD II II II II It II TR Turn Radius ft) 2 3 4 5 6 7 8 9 10 11 12 13 14 lb lb 1! MAXIMUM OFFTRACKING (feet) FIGURE E-7 Maximum offtracking for STAA twin trailer truck (conventional cab) on turns of varying geometry (Caltrans).
180 150 120 a) Ul 0 90 z cc 60 30 - C) CJ II II II II I, Cr ci cc F- TR = Turn Radius (ft) I I I I I I i I I - 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 MAXIMUM OFFTRACKING (feet) FIGURE E-8 Maximum offtracking for 48-ft tractor-semitrailer (conventional cab) on turns of varying geometry (Caltrans).
180 150 120 Im 'U -J 90 z z 60 30 0 -Q -o 8 - U) C) U) 0 C) 01 01 - II II II II II Is Cc . Cr Iâ Iâ - Iâ Iâ â¢1 - Ilk TR = Turn Radius (ft) _I_ I_ _ i__ I 2 3 4 5 6 7 8 9 10 11 1 13 1+ 13 D it MAXIMUM OFFTRACKING (feet) FIGURE E-9 Maximum offtracking for 48-ft tractor-semitrailer (California cab) on turns of varying geometry (Caltrans).
180 150 120 0 90 60 li II ) i Ni Ci 7 II I cc I I I I I 30 TR = Turn Radius (ft) 0 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 MAXIMUM OFFTRACKING (feet) FIGURE E-10 Maximum offtracking for 53-ft tractor-semitrailer (conventional cab) on turns of varying geometry (Caltrans).
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 15 17 15 1 U ZI ZZ ZJ 44 40 40 ef o .'.' MAXIMUM OFFTRACKING (feet) FIGURE E-11 Maximum offtracking for 59-ft tractor-semitrailer (conventional cab) on turns of varying geometry (Caltrans).
60 75 15 0 0 - - 0 0 CD Cr ft If II I- F- I- R:Turn Radius () 4.0 J :3.5 4 4.5 MAXIMUM OFFTRACKING (feet) FIGURE E41 (continued)
297 semitrailer needs 12.6 ft. Finally, compare these pavement requirements with the actual lane and shoulder width available.7 Idaho has also developed graphic representations of the maximum offtracking of several design vehicles for a range of truck turning radii and provided accompanying design guidelines for minimum pavement widths. Calculating Offtracking at Intersections Although the computer tabulations provide a measure of offtracking of trucks turning at intersections, if these measures are used in the manner just described to compute the swept path width, they often overstate the amount of lane encroachment that will occur. Highway design engineers typically lay templates developed from these computer runs over intersec- tion schematics, lining up the path of the truck turn with the curb return line, to determine more precisely how much the truck will actually en- croach into other lanes during the turn. This method takes into account adjustments that truck drivers normally make in approaching intersection turns. Figures E-12 and E-13 show templates, which can be applied to a range of intersection curves assuming a 50- and a 60-ft turn radius, for a 48-ft tractor-semitrailer with its rear axles in the farthest back position. Effective intersection capacity can also be increased through such measures as changes in signalization, which allow trucks to take advan- tage of gaps in the traffic stream to negotiate turns,8 and setting back the stop line and removing parking on the roadway into which the truck turns to allow the truck to use the parking lane.9 Despite these measures, there are physical limitations, given the size of the truck and the geometrics of the intersection, that preclude turning moves without major intersection improvements. New vehicle technologies are being developed that may also help improve vehicle maneuverability. The steerable axle, a stationary trailer axle that is separated from the following rear trailer axle by a distance sufficient to allow each to operate as a single axle, has the effect of substantially shortening the effective trailer wheelbase and thereby re- ducing low-speed offtracking. HOwever, more widely spread axles in- crease friction requirements, particularly on wet surfaces during tight turning maneuvers (Fancher and Mathew 1988, 35). For these reasons, such technological solutions are still in the development phase.
B 2 909 0 .n STAA TRUCK SEMITRAILER WHEEL TRACKS SCALE IN FEET 0 50 100 150 15.1-I_I- FIGURE â¢E-12 Intersection turning template for STAA 48-ft tractor- semitrailer, 50-ft turn radius (Caltrans). -
2 4b0 . 900 0 All i STAA TRUCK SEMITRAILER WHEEL TRACKS SCALE IN FEET 0 50 100 150 now FIGURE E-13 Intersection turning template for STAA 48-ft tractor- semitrailer, 60-ft turn radius (Caltrans).
300 NOTES Technically, offtracking is defined as the lateral deviation of the path of the center of the steering axle from the path of the center of the last axle. Swept path width is the offtracking amount plus half of the width of the steering axle (i.e., from the center of the axle to the outside edge) plus half of the width of the last axle. These distinctions are important because the width of the steering axle is usually less than that of the last axle. High-speed offtracking increases as a function of speed and of the number of trailing units and thus is a greater problem for STAA twin trailer trucks than for STAA tractor-semitrajlers. High-speed offtracking is also a function of suspension and tire characteristics of the vehicle and of superelevation of the road cross section in the turn; superelevation lessens high-speed offtracking but amplifies low-speed offtracking (personal com- munication with W. D. Glauz and D. W. Harwood, Midwest Research Institute, January 26, 1989). The model is available from Caltrans Truck Operations Branch, Caltrans, 1120 N Street, Sacramento, California 95814. Efforts to modify the model for use on personal computers are under way and will be completed by early 1990. Turn radii for 400 to 1,000 ft are shown in Figure E-11 for the 59-ft tractor- semitrailer to illustrate that the long wheelbase of the 59-ft semitrailer can increase offtracking even on these gentler turns for turn angles of less than 45 degrees. Different assumptions can be made about vehicle width depending on the dimen- sions of the vehicles actually on the road. If the improved shoulder is also considered in the required pavement width calcula- tion, slightly smaller turn radii could be tolerated. Removing signalization at intersections with more than minimal right-turning trucks or moving back the stop line and traffic light on the roadway into which the trucks turn should increase intersection capacity (DeCabooter and Solberg 1989, 18, 23). Parking along the first 200 ft of the critical lanes into which the truck turns, that is, on the lane on the truck's passenger side for a left-turning truck and the lane on the truck driver's side for a right-turning truck, can interfere with trucks' completing their turning maneuvers (DeCabooter and Solberg 1989, 24). REFERENCES ABBREVIATIONS AASHTO American Association of State Highway and Trans- portation Officials. FHWA Federal Highway Administration TRB Transportation Research Board AASHTO. 1984. A Policy on Geometric Design of Highways and Streets. Wash- ington, D.C.
301 DeCabooter, P. H., and C. E. Solberg. 1989. Geometric Considerations Relating to Long Truck Operations on the Designated Highway System in Urban Areas. In Transportation Research Record. TRB, National Research Council, Wash- ington, D.C., forthcoming. Ervin, R. D., andY. Guy. 1986. The Influence of Weights and Dimensions on the Stability and Control of Heavy-Duty Trucks in Canada, Vol. 1: Technical Report. UMTRI-86-3511. The University of Michigan Transportation Research Institute, Ann Arbor, July, 277 pp. Fambro, D. B., J. M. Mason, and N. S. Cline. 1988. Intersection Channelization Guidelines for Longer and Wider Trucks. Transportation Research Record. TRB, National Research Council, Washington, D.C., forthcoming. Fancher, P. S., and A. Mathew. 1988. Safety Implications of Various Truck Configurations, Vol 1: Technical Report. FHWA-RD-89-018. The University of Michigan Transportation Research Institute, Ann Arbor; FHWA, U.S. De- partment of Transportation, Dec., 268 pp. Fong, K.T., and D.C. Chenu. 1986. Simulation of Truck Ttirns with a Computer Model. In Transportation Research Record 1100. TRB, National Research Council, Washington, D.C., pp. 20-29. Guide for Monitoring and Enhancing Safety on the National Truck Network. 1986. FHWA, U.S. Department of Transportation, Oct., 58 pp. TRB. 1986. Twin Trailer Trucks. Special Report 211. National Research Council, Washington, D.C., 388 pp.
APPENDIX F Pavement Rehabilitation Cost Model This appendix provides a brief description of the pavement rehabilitation cost model used in Chapter 8 to estimate the impact on pavement service life and rehabilitation costs of an increase in axle loads on a typical arterial access highway.' The model provides cost estimates for flexible and rigid pavement, but only the former is described here because the-example in Chapter 8 is based on a flexible pavement. ELEMENTS OF THE MODEL The model incorporates the overlay design procedures recommended by AASHTO (AASHTO 1986) for determining overlay thickness require- ments and the time remaining before in-service pavements require reha' bilitation. The example developed in Chapter 8 was based on the design assumptions listed in Table F-i. The cost components of the model include both fixed-cost and variable- cost elements. The fixed-cost elements reflect factors that are indepen- dent of overlay thickness such as application of leveling courses, milling, joint repair, subdrainage improvements, and traffic control. The variable- cost element is driven by the quantity of overlay materials required, which is a function of overlay thickness, number of lanes, and lane and shoulder width. Each added axle load, measured as equivalent single axle loads (ESALs), affects overlay thickness and thus variable costs. In addition, each added axle load shortens the normal rehabilitation interval; thus the fixed element of overlay cost is also affected. Table F-i gives the cost assumptions that underlie the cost estimates in the example in Chapter 8. 303
304 TABLE F-i PAVEMENT REHABILITATION COST MODEL ASSUMPTIONS AND INPUTS Assumption Value Design Assumptions Minimum overlay thickness 2 in. Terminal serviceability 2.5 PSI Rehabilitation interval 12 year Restore pavement condition to 4.2 PSI Present serviceability index 3.4 Structural number 4 Subgrade modulus of resilience 6,250 psi Annual design-lane ESALs 81,550 to 100,100 Cost Assumptions Fixed costs $90,000/mi Variable costs $15,000/in./mi' Number of lanes 2 Lane width 12 ft Shoulder width 4 ft NOTE: PSI = Present Serviceability Index psi = pounds per square inch This cost assumes in-place costs of asphalt concrete of $25 to $30 per ton Pavement rehabilitation is a recurring activity the costs of which can be considered periodic future lump-sum expenditures. When traffic loading is accelerated, the next rehabilitation is required sooner, rehabilitation costs are increased, and the normal rehabilitation interval is shortened. The cost model converts a single lump-sum cost for each rehabilitation cycle, which is assumed to recur indefinitely into the future, into uniform annual cost equivalents using a discount factor of 7 percent. SENSITIVITY ANALYSIS The incremental pavement rehabilitation costs that result from added ESALs are primarily affected by the level of traffic and the present condition of the pavement. As Figure F-i shows,2 when traffic is light, the marginal effect of heavy trucks on rehabilitation costs, measured in cents per ESAL-mile, is much greater than when traffic is heavy. Marginal rehabilitation costs due to increased traffic loading are also affected by the present condition of the pavement. Added ESALs impose larger rehabilitation costs on new than on worn pavement surfaces (Figure F-2).
0 .8 .6 Uj .4 .2 0 0 1 2 3 4 ANNUAL DESIGN-LANE ESALS (Millions) FIGURE F-i Sensitivity of marginal unit cost of pavement rehabilitation to level of pavement loadingâtypical flexible pavement. 1500 1200 900 Z 600 0 0 300 z 0' 2.8 3 3.2 3.4 3.6 PRESENT SERVICEABILITY INDEX FIGURE F-2 Sensitivity of added cost of pavement rehabilitation for a 10 percent loading increment to existing pavement conditionâtypical flexible pavement.
306 Marginal rehabilitation costs are relatively insensitive to the effects of other pavement design variables, such as structural number and subgrade modulus of resilience. ENVIRONMENTAL EFFECTS The effect of environmental factors was also considered in developing the cost model. Environmental factors may be grouped into two categories: those that cause deterioration that is independent of traffic loading and those that interact with axle loading to affect the pavement. The effect of non-load-related environmental factors was examined in a sensitivity analysis. Examples of these effects are thermal cracking, aging of materials, differential heaving caused by swelling subgrades or frost penetration, and disintegration of bound surfacing materials as a result of freeze-thaw cycles. Use of deicing chemicals and inferior construction materials may also contribute to loss of serviceability. Loss in ser- viceability of an overlaid pavement during its rehabilitation cycle was assumed to be the effect of two components, an environmental compo- nent and a traffic component. To determine the effect on marginal pave- 1500 1200 I ::: 300 .2 ENVIRONMENTAL SERVICEABILITy' LOSS IN 12 YEARS FIGURE F-3 Sensitivity of added cost of pavement rehabilitation for a 10 percent loading increment to level of environmental serviceability lossâtypical flexible pavement.
307 ment rehabilitation costs, the environmental component was varied so that environmental serviceability loss at the end of the 12-year cycle varied from zero, or no environmental degradation, to one, or a 67 percent loss of total pavement serviceability attributable to environmen- tal factors. As Figure F-3 shows, the incremental rehabilitation costs attributable to heavier axle loads are not sensitive to environmental factors except under the most severe conditions. A 10 percent increase in ESALs results in a 23 percent greater rehabilitation expenditure for the most severe environmental condition than for that of no environmental damage. Load-related environmental factors, such as the effects of moisture on the stiffness and strength of clay subgrades and the susceptibility of asphalt concrete stiffness to temperatUre, were also examined. Only one factor, the subgrade modulus of resilience, is affected by the environment (rainfall and temperature). The AASHTO design guide provides a crude means of adjusting for these effects, but only on low-volume roads. NOTES The material for this appendix was taken from an unpublished paper by Jack Deacon entitled Pavement Rehabilitation Cost Model prepared for the Transporta- tion Research Board and revised October 1, 1988. Figures F-i, F-2, and F-3 are based on input assumptions representative of a four- lane highwayâannual design-lane ESALs, 2.5 million; structural number, 6; termi- nal serviceability, 2.7; present serviceability index, 2.8; fixed costs, $150,000/mi; and variable costs, $30,000/in/mi (12-ft lanes plus inside and outside shoulders of 7.5 ft). The relationships, however, should be the same if the model is adjusted to reflect a two-lane highway more typical of access roads. REFERENCE ABBREVIATION AASHTO American Association of State Highway Transportation Officials AASHTO. 1986. AASHTO Guide for Design of Pavement Structures. Washing- ton, D.C.
APPENDIX G Dissenting Statement I am unable to concur in the report of the Committee without these qualifications. My reasons are these: The report does not give due regard to overall safety. I believe our charge is to make recommendations that promote overall safety. Every denial of a direct access route has possible negative safety consequences; the vehicle will take a circuitous route, or more small vehicles will be substituted, with the result of more accident exposure. If you increase miles of operation, you increase accidents. The report neglects this and invites states to neglect it. The report also reflects a contradiction that has not been resolved. The Committee recognized that an important difference between some STAA vehicles and non-STAA vehicles would be offtracking. Other differences are slight, immaterial or largely hypothetical or relate to large commercial vehicles generally. The Committee rejected, however, controlling access by limiting vehicle offtracking by regulating the wheelbases of both tractor and trailer. Instead, the Committee recommended limiting only trailer wheelbase. Though trailer wheelbase is the largest factor, varia- tions in tractors can cause large variations in offtracking. This is partic- ularly true because tractors with 280" and large wheelbases are being introduced. This means that STAA vehicles cannot be treated as a generic class. They vary widely in characteristics, most pertinently in offtracking. The report, however, lumps all STAA vehicles together as one generic class, despite recognizing the wide variance. This creates bad policy. Should a poor geometry road be denied a twin trailer (the best offtracking vehicle) because its geometry is unsuitable for a long tractor wheelbase semi-trailer combination? Similarly should a route be denied a semi-trailer with a short wheelbase tractor because the same trailer with a long wheelbase tractor would have bad offtracking? 309
310 That is not reasonable. The lumping together leads states to deny access routes to safe vehicles. The state may deny access to a vehicle with good performance characteristics because it is an "STAA" vehicle and other "STAA" vehicle of totally different configuration and size might have trouble on that road. The particular STAA vehicle at issue may even have better off tracking characteristics than non-STAA vehicles the state allows on all roads. The report invites banning access for vehicles with good characteristics, thereby denigrating safety, because it treats all STAA vehicles as one class. States will thus have to judge all STAA vehicles as if they were èoupled to long wheelbase tractors. The end result will be a denigration of overall safety. For these reasons I am unable to concur in the report of the Committee majority. Date: April 6, 1989 Donald F. Kuster
Study Committee Biographical Information ROLAND A. OUELLETTE, Chairman, is President of the Eno Foundation for Transportation. He received his bachelor's degree from St. Anselm's College. Before assuming his current position he served on the Founda- tion's Board of Directors for 7 years and was Director of Transportation Affairs for the Washington, D.C., office of General Motors Corporation, which he joined in 1968. He had previously served in executive positions with the Transportation Association of America and the Chamber of Commerce of the United States and as U.S. Senate Commerce Commit- tee Staffing Coordinator of the 1961 National Transportation Policy Study that formed the legislative basis for the creation of the Department of Transportation. He is Past Chairman of the Transportation Committee of the Motor Vehicles Manufacturers Association and has served on the Executive Committee of the Transportation Research Board. ROBERT G. ADAMS has recently retired as Deputy Director of Highway Maintenance and Transportation Operations, California Department of Transportation. He holds a bachelor's degree in civil engineering from the University of Minnesota. After joining the California Department of Transportation as an engineer, he served as Assistant Director of Finan- cial Management, Chief of the Division of Project Development, and Chief of the Division of Highways. He was a member of TRB's Commit- tee on Twin Trailer Trucks. CAiuA J. BERROYER is the Deputy Director of Intergovernmental Affairs for the Illinois Department of Transportation. She received her bachelor's degree from the University of Illinois at Chicago. Since joining the Illinois 311
312 Department of Transportation, she has held several positions, including Chief of Safety Project Evaluation, Senior Policy Specialist, and Assistant to the Director of the Division of Highways. Currently, she is Chairperson of the Illinois Motor Carrier Advisory Committee and member of the Congressional Office of Technology Assessment's Advisory Panel on Motor Carrier and Airline Safety. She is also a state representative on the National Governors Association's Transportation Committee and the American Association of State Highway and Transportation Officials' Policy Committee. BYRON C. BLASCHKE is the Deputy Engineer-Director of the Texas De- partment of Highways and Public Transportation. He holds a bachelor's degree in civil engineering from Texas A&M University. He has been with the Texas Department of Highways since 1963, holding the positions of Chief Engineer in the Safety and Maintenance Operations Division, Chief Engineer of the Highway Design Division, and Deputy Director of Design and Construction. He has served TRB as Chairman of the Long- Term Pavement Performance Advisory Committee and on the Strategic Highway Research Program's Overview Committee. In 1987 he was presented the President's Modal Award for Highways by the American Association of State Highway and Transportation Officials. JOHN W. BOORSE is a transportation consultant with Parsons Brinckerhoff, Inc. He has a bachelor's degree in civil engineering from Drexel Univer- sity. Before assuming his current position, he was the Chief Traffic Engi- neer for the City of Philadelphia, where he worked for more than 30 years in various positions, including Assistant Operations Engineer, Traffic Investigation Engineer, and Assistant Chief Traffic Engineer. He has been a guest lecturer at Carnegie-Mellon University and is a member of the American Society of Highway Engineers and the Institute of Trans- portation Engineers. S. EARL DOVE is Chairman of AAA Cooper Transportation, a regional less-than-truckload carrier based in Alabama. He received his bachelor's degree in Transportation Studies from the University of Tennessee. He has worked for AAA Cooper since 1955 and became Chairman in 1972. He is Past Chairman of the American Trucking Associations and the Alabama Trucking Association. In addition, he has served as a member of the Board of Governors' Regular Common Carriers Conference and Regional Common Carriers Conference. He is currently a member of the Policy and Finance Committee and Chairman of the Regulatory Policy
313 Committee of the American Trucking Associations. He serves on TRB's Committee on Urban Goods Movement and is a newly appointed mem- ber of TRB's Executive Committee. WILLIAM D. GLAUZ is the Director of the Engineering and Materials Science Department at the Midwest Research Institute. He holds a bache- lor's degree from Michigan State University and a master's degree and Ph.D. in engineering sciences from Purdue University. He has held several positions at the Midwest Research Institute, including Manager of the Transportation Systems Center and Assistant Director of the Division of Engineering. He currently serves on TRB's Group 3 Council on Operations, Safety, and Maintenance of Transportation Facilities, and committees on Motor Vehicle Size and Weight, on Methodobolgy for Evaluating Highway Improvements, and on Traffic Law Enforcement. He previously served on TRB's Committee on Twin Trailer Trucks. JEROME W. HALL is Professor of Civil Engineering and was Associate Dean of Engineering from 1985 to 1988 at the University of New Mexico. He received his bachelor's degree from Harvey Mudd College and a master's degree and Ph.D. in civil engineering from the University of Washington. Before joining the University of New Mexico in 1977, he was an Associate Professor of Civil Engineering at the University of Mary- land. From 1981 to 1985 he directed the University of New Mexico's Bureau of Engineering Research. He is Chairman of the TRB Committee on Operational Effects of Geometrics and was a member of the TRB Task Force on Incompatibilities Among the Vehicle, Driver and Highway. He is also a fellow of the Institute of Transportation Engineers (ITE) and Vice President of ITE District 6. GEORGE W. HERNDON is Manager of Regulatory and Federal Policies of the Office of Policy of the Florida Department of Transportation. He received a bachelor's degree from Western Kentucky University and a master's degree in public administration from the University of Oklahoma. After retiring from the U.S. Army in 1974, he joined the Florida Department of Transportation as a strategic planner. He has been a member of the National Governors Association's Working Group on State Motor Car- rier Procedures and has served as a state representative on the American Association of State Highway and Transportation Officials' Studies on Motor Carrier Taxation Issues and the Future of the Federal Highway System.
314 Vtr 'CLEVE HOLMES is a Lieutenant and Assistant Commander of the Truck Enforcement Division of the Maryland State Police, responsible for enforcing'federal and state truck safety regulations and laws. He received a bachelor's degree in administration of justice from American Univer- sity. Before joining the Truck Enforcement Division in 1984, he worked for 15.years on road patrol and telecommunications assignments for the Maryland State Police. DONALD F. KUSTER is a Vice President of Hermann Services, Inc., in charge of sales and marketing. Previously, he was General Manager of Traffic and Distribution for Continental Can Company, where he worked for more than 30 years in positions related to shipping and distribution. He is Past President of the National Industrial Transportation League and helped establish the 60 NR Committee, a group of shippers and carriers concerned with trucking legislation. He is Past Chairman of the League's Highway Facilities Committee and has served on the American Trucking Associations' Committee on Deregulation. HAROLD L. MICHAEL is Head of the School of Civil Engineering and Director of the Joint Highway Research Project at Purdue University. He received his bachelor's and master's degrees in civil engineering from Purdue University. Before becoming Head of the School of Civil Engi- neering in 1978, he served many years as Professor of Highway Engineer- ing and Head of Transportation and Engineering. He is a member of the National Academy of Engineering, Past President of the Institute of Transportation Engineers, Past Director of the National Society of Profes- sional Engineers, and Past Member of the Board of Consultants of the Eno Foundation for Transportation. He has previously served TRB as Chairman of the Executive Committee, Chairman of Division A Council, and Chairman of Group 3 Council, Operations and Maintenance. He is currently a member of the Board of Executives of the Strategic Highway Research Program. WILLIAM A. PHANG is a research consultant with Pavement Management Systems of Amherst, New York. He holds a bachelor's degree from the University of London and a master's degree in civil engineering from Purdue University. Before assuming his current position, he was Head of Pavement Research for the Ontario Ministry of Transportation, having served as Development Engineer in the Materials and Testing Office and as a research engineer in the Ministry's Department of Highways. He is
315 currently Chairman of the Design Management Committee and a mem- ber of the Technical Steering Committee on Vehicle Weights of the Roads and Transportation Association of Canada. JAMES P. RAKOWSKI is Professor of Marketing in the College of Business and Economics at Memphis State University. He received his bachelor's degree in economics from Princeton University and a Ph.D. in business administration from Columbia University. Before joining the faculty of Memphis State in 1978, he was an Assistant Professor of Management in the School of Business at the University of Minnesota. He has published numerous articles on pricing, regulation, and marketing issues related to the trucking industry. MICHAEL J. RIGHT is the Director of Public Affairs for the Automobile Club of Missouri and Editor of Midwest Motorist. Before joining the Automobile Club in 1966, he worked as a traffic investigator for the City of St. Louis. He is a member of the Environment, Energy, and Highway Committees of the American Automobile Association and is Past Presi- dent of the St: Louis Traffic Law Enforcement Organization and the Traffic Engineers Association of Metropolitan St. Louis. CHESTER STRANCZEK is Chairman of Cresco Lines, Inc., a national truck- load carrier based in Illinois. He is active in national and state trucking and transportation organizations, having served as Vice Chairman of the American Trucking Associations and Chairman of the Interstate Carrier Conference, and as a member of the Illinois Trucking Association and the Regional Transportation Board of Illinois. He is also Mayor of Crest- wood, Illinois. GERALD STREICHERT is a construction engineer with the Shawassee County Road Commission in Michigan. He has a bachelor's degree in civil engineering from the Michigan Technological University. Before joining the Shawassee County Road Commission in 1985, he worked for more than 30 years for the Genesee County Road Commission in Michigan as Director of Operations and engineer in the road design and construction divisions. He is Past President of the County Road Superintendents Association of Michigan and is currently Northeast Vice President of the National Association of County Engineers. CHARLES V. ZEGEER is a Staff Associate with the Highway Safety Re- search Center of the University of North Carolina. He received his
316 bachelor's degree from Virginia Polytechnic Institute and State Univer- sity and a master's degree in engineering from the University of Ken- tucky. Between 1979 and 1986, he served as Director of Traffic and Safety for Goodell-Grivas, Inc., and later as Vice President. Previously he worked as a research engineer with the Bureau of Highways of the Kentucky Department of Transportation. He is currently chair of Section B of TRB's Group 3 Council and serves on TRB's committees on the Operational Effects of Geometrics and on Traffic Records and Accident Analysis.
1989 TRANSPORTATION RESEARCH BOARD EXECUTIVE COMMITTEE Chairman: Louis J. Gambaccini, General Manager, Southeastern Pennsylvania Transportation Au- thority (SEPTA), Philadelphia Vice Chairman: Wayne Muri, Chief Engineer, Missouri Highway & Transportation Department, Jefferson City Executive Director. Thomas B. Deen, Transportation Research Board Adm. James B. Buscy IV, Administrator-designate, Federal Aviation Administration, U.S. Department of Transportation (ex officio) Brian W. clymer, Administrator-designate, Urban Mass Transportation Administration, U.S. Depart- ment of Transportation (ex officio) Jerry R. Curiy, Administrator-designate, National Highway Traffic Safety Administration, U.S. Depart- ment of Transportation (ex officio) Francis B. Francois, Executive Director, American Association of State Highway and Transportation Officials, Washington, D.C. (ex officio) John Gray, President, National Asphalt Pavement Association, Riverdale, Maryland (ex officio) Thomas H. Hanna, President and Chief Executive Officer, Motor Vehide Manufacturers Association of the United States, Inc., Detroit, Michigan (ex officio) LI Cen. Henry J. Hatch, Chief of Engineers and Commander, U.S. Army Corps of Engineers, Washington, D.C. (ex officio) Thomas D. Larson, Administrator-designate, Federal Highway Administration, U.S. Department of Transportation (ex officio) George H. Way, Jr., Vice President, Research and Test Department, Association of American Railroads, Washington, D.C. (ex officio) Robert J. Aamnson, President, Air Transport Association of America, Washington, D.C. Robert N. Bothman, Director, Oregon Department of Transportation, Salem J. Ron Brinson, President and Chief Executive Officer, Board of Commissioners of the Port of New Orleans, Louisiana L. Gary Byrd, Consultant Engineer, Alexandria, Virginia John A. Clements, Vice President, Parsons Brinckerhoff Quade and Douglas, Inc., Boston, Mas- sachusetts (Past Chairman, 1985) Susan C. Crampton, Secretary of Transportation, State of Vermont Agency of Transportation, Montpelier L. Stanley Crane, Suburban Station Building, Philadelphia, Pennsylvania Randy Doi, Director, IVI-IS Systems, Motorola Inc., Northbrook, Illinois S. Earl Dove, Chairman of the Board, AAA Cooper Transportation, Dothan, Alabama William J. Harris, E. B. Snead Professor of Transportation Engineering and Distinguished Professor of Civil Engineering, Associate Director of Texas Transportation Institute, Texas A&M University System, College Station Lowell B. Jackson, Vice President for Transportation, Grecnhorne & O'Mara, Inc.. Greenbelt, Maryland (Past Chairman, 1987) Denman K. McNear, Vice Chairman, Rio Grande Industries, San Francisco, California Leno Mcnghini, Superintendent and Chief Engineer, Wyoming Highway Department, Cheyenne William W. Millar, Executive Director, Port Authority of Allegheny County, Pittsburgh, Pennsylvania Robert E. Paaswell, Professor, Transportation Engineering, Urban Transportation Center, University of Illinois, Chicago Ray D. Pcthtel, Commissioner, Virginia Department of Transportation, Richmond James P. Pitz, Director, Michigan Department of Transportation, Lansing Herbert H. Richardson, Deputy Chancellor and Dean of Engineering, Texas A&M University System, College Station (Past Chairman, 1988) Joe C. Rideouette, Executive Director, South Carolina Department of Highways and Public Transpor- tation, Columbia Ted Tcdesco, Vice President, Corporate Affairs, American Airlines, Inc., Dallas/Fort Worth Airport, Texas Carmen E. Turner, General Manager, Washington Metropolitan Area Transit Authority, Washington, D.C. C. Michael Walton, Bess Harris Jones Centennial Professor of Natural Resource Policy Studies and Chairman, College of Engineering, The University of Texas at Austin Franklin E. White, Commissioner, New York State Department of Transportation, Albany Julian Wolpert, Henry G. Bryant Professor of Geography, Public Affairs and Urban Planning, Wood- row Wilson School of Public and International Affairs, Princeton University, New Jersey Paul Zia, Distinguished Professor, Department of Civil Engineering, North Carolina State University, Raleigh
The Transportation Research Board is a unit of the National Researci- Council, which serves the National Academy of Sciences and the National Acad- emy of Engineering. The Board's purpose is to stimulate research concerning the nature and performance of transportation systems, to disseminate the information produced by the research, and to encourage the application of appropriate research findings. The Board's program is carried out by more than 300 committees, task forces, and panels composed of more than 3,500 administrators, engineers, sochi scientists, attorneys, educators, and others concerned with transportation; the serve without compensation. The program is supported by state transportation an highway departments, the modal administrations of the U.S. Department of Trans- portation, and other organizations and individuals interested in the development of transportation. The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical mattters. Dr. Frank Press is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibi'ity for advising the federal government. The National Academy of Engineerg also sponsors engineering programs aimed at meeting national needs, encourag education and research, and recognizes the superior achievements of engineers Dr. Robert M. White is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. D:. Samuel 0. Thier is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and advising the federal govern- ment. Functioning in accordance with general policies detennined by the Acad emy, the Council has become the principal operating agency of both the Nationa Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering commu nities. The Council is administered jointly by both the Academies and the Institut of Medicine. Dr. Frank Press and Dr. Robert M. White are chairman and vie chairman, respectively, of the National Research Council.
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