National Academies Press: OpenBook

Development of Clear Recovery Area Guidelines (2024)

Chapter: Front Matter

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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2024. Development of Clear Recovery Area Guidelines. Washington, DC: The National Academies Press. doi: 10.17226/27593.
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2024 N A T I O N A L C O O P E R A T I V E H I G H W A Y R E S E A R C H P R O G R A M NCHRP RESEARCH REPORT 1097 Development of Clear Recovery Area Guidelines Roger Bligh Boniphace Kutela Sofokli Cakalli Nauman Sheikh Raul Avelar Texas A&M Transportation Institute The Texas A&M University System College Station, Texas Subscriber Categories Design • Operations and Trafc Management • Safety and Human Factors Research sponsored by the American Association of State Highway and Transportation Ofcials in cooperation with the Federal Highway Administration

NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Systematic, well-designed, and implementable research is the most effective way to solve many problems facing state departments of transportation (DOTs) administrators and engineers. Often, highway problems are of local or regional interest and can best be studied by state DOTs individually or in cooperation with their state universities and others. However, the accelerating growth of highway transporta- tion results in increasingly complex problems of wide interest to high- way authorities. These problems are best studied through a coordinated program of cooperative research. Recognizing this need, the leadership of the American Association of State Highway and Transportation Officials (AASHTO) in 1962 ini- tiated an objective national highway research program using modern scientific techniques—the National Cooperative Highway Research Program (NCHRP). NCHRP is supported on a continuing basis by funds from participating member states of AASHTO and receives the full cooperation and support of the Federal Highway Administration (FHWA), United States Department of Transportation, under Agree- ment No. 693JJ31950003. The Transportation Research Board (TRB) of the National Academies of Sciences, Engineering, and Medicine was requested by AASHTO to administer the research program because of TRB’s recognized objectivity and understanding of modern research practices. TRB is uniquely suited for this purpose for many reasons: TRB maintains an extensive com- mittee structure from which authorities on any highway transportation subject may be drawn; TRB possesses avenues of communications and cooperation with federal, state, and local governmental agencies, univer- sities, and industry; TRB’s relationship to the National Academies is an insurance of objectivity; and TRB maintains a full-time staff of special- ists in highway transportation matters to bring the findings of research directly to those in a position to use them. The program is developed on the basis of research needs iden- tified by chief administrators and other staff of the highway and transportation departments, by committees of AASHTO, and by the FHWA. Topics of the highest merit are selected by the AASHTO Special Committee on Research and Innovation (R&I), and each year R&I’s recommendations are proposed to the AASHTO Board of Direc- tors and the National Academies. Research projects to address these topics are defined by NCHRP, and qualified research agencies are selected from submitted proposals. Administration and surveillance of research contracts are the responsibilities of the National Academies and TRB. The needs for highway research are many, and NCHRP can make significant contributions to solving highway transportation problems of mutual concern to many responsible groups. The program, however, is intended to complement, rather than to substitute for or duplicate, other highway research programs. Published research reports of the NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM are available from Transportation Research Board Business Office 500 Fifth Street, NW Washington, DC 20001 and can be ordered through the Internet by going to https://www.mytrb.org/MyTRB/Store/default.aspx Printed in the United States of America NCHRP RESEARCH REPORT 1097 Project 17-11(03) ISSN 2572-3766 (Print) ISSN 2572-3774 (Online) ISBN 978-0-309-70945-3 Library of Congress Control Number 2024931083 © 2024 by the National Academy of Sciences. National Academies of Sciences, Engineering, and Medicine and the graphical logo are trade- marks of the National Academy of Sciences. All rights reserved. COPYRIGHT INFORMATION Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. Cooperative Research Programs (CRP) grants permission to reproduce material in this publication for classroom and not-for-profit purposes. Permission is given with the understanding that none of the material will be used to imply TRB, AASHTO, APTA, FAA, FHWA, FTA, GHSA, or NHTSA endorsement of a particular product, method, or practice. It is expected that those reproducing the material in this document for educational and not-for-profit uses will give appropriate acknowledgment of the source of any reprinted or reproduced material. For other uses of the material, request permission from CRP. NOTICE The research report was reviewed by the technical panel and accepted for publication according to procedures established and overseen by the Transportation Research Board and approved by the National Academies of Sciences, Engineering, and Medicine. The opinions and conclusions expressed or implied in this report are those of the researchers who performed the research and are not necessarily those of the Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; the FHWA; or the program sponsors. The Transportation Research Board does not develop, issue, or publish standards or spec- ifications. The Transportation Research Board manages applied research projects which provide the scientific foundation that may be used by Transportation Research Board sponsors, industry associations, or other organizations as the basis for revised practices, procedures, or specifications. The Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; and the sponsors of the National Cooperative Highway Research Program do not endorse products or manufacturers. Trade or manufacturers’ names or logos appear herein solely because they are considered essential to the object of the report.

e National Academy of Sciences was established in 1863 by an Act of Congress, signed by President Lincoln, as a private, non- governmental institution to advise the nation on issues related to science and technology. Members are elected by their peers for outstanding contributions to research. Dr. Marcia McNutt is president. e National Academy of Engineering was established in 1964 under the charter of the National Academy of Sciences to bring the practices of engineering to advising the nation. Members are elected by their peers for extraordinary contributions to engineering. Dr. John L. Anderson is president. e National Academy of Medicine (formerly the Institute of Medicine) was established in 1970 under the charter of the National Academy of Sciences to advise the nation on medical and health issues. Members are elected by their peers for distinguished contributions to medicine and health. Dr. Victor J. Dzau is president. e three Academies work together as the National Academies of Sciences, Engineering, and Medicine to provide independent, objective analysis and advice to the nation and conduct other activities to solve complex problems and inform public policy decisions. e National Academies also encourage education and research, recognize outstanding contributions to knowledge, and increase public understanding in matters of science, engineering, and medicine. Learn more about the National Academies of Sciences, Engineering, and Medicine at www.nationalacademies.org. e Transportation Research Board is one of seven major program divisions of the National Academies of Sciences, Engineering, and Medicine. e mission of the Transportation Research Board is to mobilize expertise, experience, and knowledge to anticipate and solve complex transportation-related challenges. e Board’s varied activities annually engage about 8,500 engineers, scientists, and other transportation researchers and practitioners from the public and private sectors and academia, all of whom contribute their expertise in the public interest. e program is supported by state transportation departments, federal agencies including the component administrations of the U.S. Department of Transportation, and other organizations and individuals interested in the development of transportation. Learn more about the Transportation Research Board at www.TRB.org.

C O O P E R A T I V E R E S E A R C H P R O G R A M S AUTHOR ACKNOWLEDGMENTS The research reported herein was performed under NCHRP Project 17-11(3) by the Texas A&M Trans- portation Institute, a member of The Texas A&M University System. CRP STAFF FOR NCHRP RESEARCH REPORT 1097 Waseem Dekelbab, Deputy Director, Cooperative Research Programs, and Manager, National Cooperative Highway Research Program David M. Jared, Senior Program Officer Mazen Alsharif, Senior Program Assistant Natalie Barnes, Director of Publications Heather DiAngelis, Associate Director of Publications NCHRP PROJECT 17-11(03) PANEL Field of Traffic—Area of Safety Don Jay Gripne, DJG NW Inc., Olympia, WA (Chair) Mark Ayton, Safe Roads R&D, Inc., Aurora, ON Drew A. Boyce, Jr., Delaware Department of Transportation, Dover, DE Mack O. Christensen, Horrocks Engineers, Pleasant Grove, UT Keith A. Cota, Epsom, NH Richard G. McGinnis, Bucknell University, Lewisburg, PA Aurora Meza, VRX, Inc., Austin, TX Aimee Zhang, FHWA Liaison

NCHRP Research Report 1097 presents guidelines to determine a recommended clear recovery distance for a given set of roadway and roadside characteristics. Due to the limita- tions inherent in using crash data for this purpose, an innovative methodology was used that combined encroachment simulations, crash data, statistical modeling, and risk analysis. The guidelines include a risk-based tool that correlates recommended clear zone distance with the potential for severe injuries or fatalities to motorists. The guidelines should be of interest to road design and safety professionals seeking to specify the safest and most practical clear zone recovery areas for various roadway designs. The clear zone concept for roadside design emerged in the mid-1960s as a single distance for lateral clearance that reduced the likelihood of an errant vehicle striking a roadside obstacle. Subsequent recovery area guidelines that developed over the next two decades provided a variable distance expressed in terms of traffic volume, design speed, sideslope, and other roadway and roadside factors. However, these values are based on studies from the 1950s through the 1980s that used relatively limited data and extrapolated numbers. User agencies saw a need for updated guidelines to aid designers in better understanding the risk associated with roadside encroachments while recognizing and working within the associated design constraints. Under NCHRP Project 17-11(03), “Development of Clear Recovery Area Guidelines,” Texas A&M Transportation Institute was asked to develop guidelines for roadside clear zones that are expressed in terms of key roadway and roadside design parameters. The research approach combined vehicle dynamics computer simulation results with crash data analyses. The vehicle dynamics simulations permitted consideration of a wide range of encroachment and design variables. Specialized crash datasets with reconstructed crashes were used to develop marginal probabilities for the encroachment variables, which were applied as weight factors to the simulation results. Statistical models were developed from the weighted simula- tion results. The statistical models were incorporated into an encroachment probability-based risk analysis tool. The analysis tool estimated the probability of a severe injury or fatal crash for a prescribed roadway and roadside configuration for a given lateral offset (i.e., clear zone distance) and a selected fixed object spacing at the clear zone edge. Clear zone guidelines were developed using a relative risk approach, whereby the recommended clear zone distance has a risk of a severe injury or fatal crash that is less than or equal to that of a roadside guardrail. The guidelines were developed using equations and a chart-based format expressed in terms of design variables found to have the most significance on the clear zone risk and hence are suitable for possible incorporation into the AASHTO Roadside Design Guide. F O R E W O R D By David M. Jared Staff Officer Transportation Research Board

1 Summary 3 Chapter 1 Introduction 5 Chapter 2 Clear Recovery Area Background 6 NCHRP Project 17-11 7 NCHRP Project 17-11(02) 8 Chapter 3 Vehicle Dynamics Encroachment Simulations 8 Simulation Code Selection 10 Vehicle Model Selection 11 Vehicle Model Development 12 Simulation Interface Manager 12 Simulation Stopping Conditions 13 Simulation Outputs 14 Non-Tracking Encroachments 16 Driver Inputs 17 Simulation Matrix 19 Chapter 4 Encroachment Variable Distributions and Marginal Probabilities 19 NCHRP Web-Only Document 341 Crash Database 19 Encroachment Parameter Distributions and Marginal Probabilities 31 Vehicle Probability Matrix 35 Chapter 5 Encroachment Relationships 35 Statistical Model Specifications and Data Generation Process 36 Lateral Extent of Encroachment Models 39 Longitudinal Distance Models 54 Impact Speed Models 59 Impact Angle Models 62 Rollover Probability Models 66 Chapter 6 Clear Zone Guideline Assistance Program 67 Framework 67 Crash Probability 74 Rollover Probability 74 Severity Prediction 78 Risk Determination 81 Chapter 7 Variable Sensitivity and Importance 81 Variable Sensitivity 116 Variable Importance C O N T E N T S

118 Chapter 8 Recovery Area Guideline Development 118 Guideline Equations 121 Guideline Charts 122 Guideline Examples 133 Chapter 9 Conclusions, Recommendations, and Suggested Research 133 Summary and Conclusions 134 For Consideration 134 Suggested Research 135 References 137 List of Abbreviations

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The clear zone concept for roadside design emerged in the mid-1960s as a single distance for lateral clearance that reduced the likelihood of an errant vehicle striking a roadside obstacle. Subsequent recovery area guidance that evolved over the next two decades provided a variable distance expressed in terms of traffic volume, design speed, sideslope, and other roadway and roadside factors.

NCHRP Research Report 1097: Development of Clear Recovery Area Guidelines, from TRB's National Cooperative Highway Research Program, develops updated guidelines for roadside clear zones expressed in terms of key roadway and roadside design parameters. These updated guidelines can aid designers in better understanding the risk associated with roadside encroachments while recognizing and working within the associated design constraints.

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