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Suggested Citation:"3. RESEARCH AND DATA RECOMMENDATIONS OF PAST STUDIES." National Academies of Sciences, Engineering, and Medicine. 2018. Truck Size and Weight Limits Research Plan Committee: First Report: Candidate Research Topics; Framework for Setting Priorities. Washington, DC: The National Academies Press. doi: 10.17226/25091.
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Suggested Citation:"3. RESEARCH AND DATA RECOMMENDATIONS OF PAST STUDIES." National Academies of Sciences, Engineering, and Medicine. 2018. Truck Size and Weight Limits Research Plan Committee: First Report: Candidate Research Topics; Framework for Setting Priorities. Washington, DC: The National Academies Press. doi: 10.17226/25091.
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Suggested Citation:"3. RESEARCH AND DATA RECOMMENDATIONS OF PAST STUDIES." National Academies of Sciences, Engineering, and Medicine. 2018. Truck Size and Weight Limits Research Plan Committee: First Report: Candidate Research Topics; Framework for Setting Priorities. Washington, DC: The National Academies Press. doi: 10.17226/25091.
×
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Suggested Citation:"3. RESEARCH AND DATA RECOMMENDATIONS OF PAST STUDIES." National Academies of Sciences, Engineering, and Medicine. 2018. Truck Size and Weight Limits Research Plan Committee: First Report: Candidate Research Topics; Framework for Setting Priorities. Washington, DC: The National Academies Press. doi: 10.17226/25091.
×
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Suggested Citation:"3. RESEARCH AND DATA RECOMMENDATIONS OF PAST STUDIES." National Academies of Sciences, Engineering, and Medicine. 2018. Truck Size and Weight Limits Research Plan Committee: First Report: Candidate Research Topics; Framework for Setting Priorities. Washington, DC: The National Academies Press. doi: 10.17226/25091.
×
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Suggested Citation:"3. RESEARCH AND DATA RECOMMENDATIONS OF PAST STUDIES." National Academies of Sciences, Engineering, and Medicine. 2018. Truck Size and Weight Limits Research Plan Committee: First Report: Candidate Research Topics; Framework for Setting Priorities. Washington, DC: The National Academies Press. doi: 10.17226/25091.
×
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Suggested Citation:"3. RESEARCH AND DATA RECOMMENDATIONS OF PAST STUDIES." National Academies of Sciences, Engineering, and Medicine. 2018. Truck Size and Weight Limits Research Plan Committee: First Report: Candidate Research Topics; Framework for Setting Priorities. Washington, DC: The National Academies Press. doi: 10.17226/25091.
×
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Suggested Citation:"3. RESEARCH AND DATA RECOMMENDATIONS OF PAST STUDIES." National Academies of Sciences, Engineering, and Medicine. 2018. Truck Size and Weight Limits Research Plan Committee: First Report: Candidate Research Topics; Framework for Setting Priorities. Washington, DC: The National Academies Press. doi: 10.17226/25091.
×
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Suggested Citation:"3. RESEARCH AND DATA RECOMMENDATIONS OF PAST STUDIES." National Academies of Sciences, Engineering, and Medicine. 2018. Truck Size and Weight Limits Research Plan Committee: First Report: Candidate Research Topics; Framework for Setting Priorities. Washington, DC: The National Academies Press. doi: 10.17226/25091.
×
Page14
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Suggested Citation:"3. RESEARCH AND DATA RECOMMENDATIONS OF PAST STUDIES." National Academies of Sciences, Engineering, and Medicine. 2018. Truck Size and Weight Limits Research Plan Committee: First Report: Candidate Research Topics; Framework for Setting Priorities. Washington, DC: The National Academies Press. doi: 10.17226/25091.
×
Page15

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5 from the conclusions that will be presented in the committee’s final report, which will be published later in 2018. RESEARCH AND DATA RECOMMENDATIONS OF PAST STUDIES The committee reviewed the research recommendations of the 2016 USDOT study and the TRB committee review of that study, the USDOT examinations of truck size and weight limits published in 2000 (FHWA 2000) and 1981 (FHWA 1981), and earlier TRB committee studies, including TRB Special Report 225, Truck Weight Limits: Issues and Options (TRB 1990), and especially TRB Special Report 267, Regulation of Weights, Lengths, and Widths of Commercial Motor Vehicles (TRB 2002), which reviewed truck size and weight studies conducted up to 2002. This section summarizes recommendations from those sources related to research and data requirements. USDOT 2016 Comprehensive Truck Size and Weight Study USDOT’s Report to Congress on its 2013–2016 study recommends numerous improvements in the data programs and in models used in the study to project the effect changes in truck size and weight limits (see Box 1). ========================================================================== BOX 1 USDOT’s 2016 Comprehensive Truck Size and Weight Study Data and Research Recommendations (FHWA 2016a, 21–25) Safety  Add truck weight and configuration data elements to state crash records  Increase geographic and highway system coverage of the data available from truck weigh-in- motion (WIM) installations  Analyze interaction of trucks over 80,000 lb. with crash barriers  Improve consistency of weight recording in state truck inspection reports

6 Enforcement  Collect more detailed data on states’ truck weight enforcement and safety enforcement costs Mode Shift, Freight Traffic  Restore the Vehicle Inventory and Use Survey (VIUS), a discontinued Census Bureau survey of truck owners  Refine USDOT’s Intermodal Transportation and Inventory Costing (ITIC) model to better reflect real-world mode choice decisions  Measure passenger car equivalents (PCEs), an index of the effect of trucks on traffic flow, for various truck configurations  Model the effect of truck size and weight limit changes on short line railroads  Disaggregate USDOT’s Freight Analysis Framework (FAF) freight flow database to provide estimated county-level freight flows by mode  Regularly collect data on shipping rates for freight carried by truck Bridges  Model the effect of changes in truck size and weight limits on bridge decks, using data from USDOT’s Long-Term Bridge Performance Program  Develop a method to estimate the effects of changes in limits on bridges on local roads Pavement  Model the effect of changes in truck size and weight limits on pavements with overlays  Collect data on local road pavement characteristics and truck traffic to support estimates of the effect of changes in limits on local roads ========================================================================== USDOT’s recommended activities are in four categories:  Adjustments or additions to existing data collection programs (truck weight in crash records; expanded WIM data; weight recording in inspection records; enforcement cost data; truck traffic data in the Long-Term Bridge Performance [LTBP] program; local bridge, pavement, and traffic data)  New periodic data collection programs (VIUS, truck shipping rates)  Narrowly focused research studies (barrier interaction of heavier trucks, large truck PCE measurement, freight flow database by county and mode, effects of changes in limits on short line railroads, refinements to ITIC) to estimate specific impacts of changing limits  New models of vehicle–infrastructure interaction (models of the effects of truck traffic on

7 bridge decks and on overlay pavements). All these could have wide applications beyond the evaluation of size and weight limits for infrastructure management The USDOT list is a catalog of the obstacles encountered in estimating impacts according to the methods chosen for the USDOT 2016 study. The list is one of the resources that the committee is using to develop the research roadmap, but it alone does not provide sufficient guidance. The recommendations do not indicate priorities among the topics and do not identify the parties with the responsibility and capacity to carry out the activities. The TRB review committee concluded that the USDOT list omits some important research needs (TRB 2015, 4–5, 20–21, 30, 35, 42, 53–54, 58). The TRB committee that USDOT asked to review the Comprehensive Truck Size and Weight Study’s technical reports was not charged with proposing a comprehensive research agenda for future truck size and weight studies. However, the committee offered some general recommendations for improving analysis capabilities (see Box 2). The committee concluded that (TRB 2015, 20–21): The research and data collection programs that would make the greatest contribution to future evaluations of truck size and weight regulations would be aimed at monitoring the impact of existing truck traffic (and changes in traffic) on highway performance and at supporting state and local highway agencies’ efforts to manage the impacts. USDOT should promote and support development and improvement of these information systems. Improvements in information systems would have the secondary benefits of supporting more credible estimates of the effects of proposed changes in truck regulations. To improve regulations, the most critical information needs are for better understanding of how truck traffic characteristics (and changes in truck traffic over time) affect (a) bridge condition and highway agency costs related to bridges and (b) highway crash and casualty risks. To project infrastructure and safety impacts of regulatory changes, information on the determinants of vehicle and mode choice is necessary.

8 =========================================================================== BOX 2 TRB’s 2015 Review of USDOT Study Data and Research Recommendations (TRB 2015, 4–5) General Purpose Information Systems  USDOT should promote improvement of state information systems that record impacts of existing truck traffic (e.g., pavement and bridge management systems, crash records) Structure of Future Truck Size and Weight Studies  Future truck size and weight studies should evaluate the full range of methods for mitigating the costs of truck traffic, including: – Size and weight limits – Vehicle design (as affecting stability and vehicle–infrastructure interaction) – Bridge and pavement design and management – Enforcement – Permit and fee systems  The objective of evaluations should be to identify strategies to reduce the public costs and increase the benefits of highway freight transportation Methods for Impact Estimates in Future Truck Size and Weight Studies  Base bridge cost estimates on explicit assumptions about state highway agency responses to changes in truck traffic  Estimate pavement and bridge impacts from valid samples of actual pavements and bridges Research  Test alternative forms of mode choice models  Continue three research efforts begun in the 2016 USDOT truck size and weight limits study: – Weigh-in-motion-derived traffic data – Relationship of crash frequency on a road to traffic volume and vehicle type mix – Relationship of weight enforcement effort to violation rate =========================================================================== The information systems to which the committee referred are those maintained by the states and federal government for basic asset management purposes: states’ asset management and safety management information systems, and federal and state data systems that support research, regulation, and planning (see Box 3). USDOT relied extensively on such information systems in the 2016 Comprehensive Truck Size and Weight Study (FHWA 2016b, Table 2).

9 =========================================================================== BOX 3 General-Purpose Information Systems Used in Truck Size and Weight Limit Evaluations Freight Traffic, Truck Use  Census Vehicle Inventory and Use Survey (VIUS)  Census Commodity Flow Survey  Surface Transportation Board Carload Waybill Sample  Federal Highway Administration (FHWA) Truck Weight Study data contained in the Vehicle Travel Information System (VTRIS)  State vehicle registration records  State traffic measurement programs (including weigh-in-motion data) Infrastructure  FHWA Long-Term Pavement Performance (LTPP) program  FHWA Long-Term Bridge Performance (LTBP) program  FHWA Highway Performance Monitoring System (HPMS)  FHWA National Bridge Inventory (NBI)  FHWA Fiscal Management Information System (FMIS)  State asset management systems Safety, Enforcement  Federal Motor Carrier Safety Administration Motor Carrier Management Information System (MCMIS)  National Highway Traffic Safety Administration Trucks in Fatal Accidents (TIFA) program  State crash record systems =========================================================================== The 2015 TRB committee’s recommendations also concerned the structure of future truck size and weight limit evaluations (TRB 2015, 4): USDOT and state research on truck regulatory policy should aim at evaluating the full range of methods for mitigating costs of truck traffic—not only size and weight limits but also changes in vehicle design; changes in bridge design, condition monitoring, and inspection practices; enforcement of dimensional and safety regulations; and design and management of truck permit and fee systems. The goal of research should be development of comprehensive strategies for improving the performance of highway freight transportation. Size and weight limits alone provide only weak leverage for improving performance. Future truck size and weight studies should be organized as

10 evaluations of comprehensive policy options rather than evaluations of alternative truck configurations. That is, the committee concluded that research needed to support truck size and weight policy decisions should not be limited to projections of the various categories of impact traditionally included in truck size and weight studies, but should include the evaluation of highway management strategies to improve system performance. Earlier Truck Size and Weight Studies The gaps in data and understanding that the 2016 USDOT study identified were recognized in earlier truck size and weight studies. The previous USDOT evaluation, published in 2000, included a list of research needs that considerably overlaps the 2016 list (see Box 4). Apparently, in the intervening years, either resources were not devoted to fulfilling the identified needs, or progress was too slow to greatly improve methods by the time of the 2016 study. =========================================================================== BOX 4 USDOT’s 2000 Comprehensive Truck Size and Weight Study: Conclusions Regarding Research and Data Needs (FHWA 2000, 39) Future research needs identified in conducting this study include: 1. Incorporating improved truck origin/destination data by commodity from the Commodity Flow Survey and other sources into the ITIC [Intermodal Transportation and Inventory Costing] freight diversion model 2. Improving other essential logistics data in the ITIC model 3. Improving our understanding of relationships between [truck size and weight] variables and truck safety risks 4. Examining the potential for new technology to reduce adverse safety and operational characteristics of current vehicles 5. Improving information on impacts of heavier vehicles on bridges and strategies to mitigate those impacts

11 6. Improving our understanding of ways to reduce traffic conflicts between large trucks and the rest of the traffic stream =========================================================================== In 2002, TRB published the committee study Regulation of Weights, Lengths, and Widths of Commercial Motor Vehicles (TRB 2002) in response to a congressional directive for a study of the federal regulation of truck sizes and weights and for recommendations on appropriate revisions. The TRB committee report reviews the major past studies of size and weight limits by the federal government, TRB, and others. The committee’s conclusions regarding the methods of truck size and weight studies (see Box 5) are applicable to the present committee’s task of designing a research plan in support of future studies. Especially relevant is the committee’s conclusion about the inevitable limitations of projections of impacts (TRB 2002, 3–4): It is not possible to predict the outcomes of regulatory changes with high confidence. Development of improved models for analyzing the costs of operating trucks of different designs would be worthwhile. However, models and data will never be adequate for providing more than plausible indications of how institutions, markets, and technology will react to regulatory changes, especially in the long run. . . . Responsible regulation is a process: the regulatory authority should do the best prior analysis possible, but once regulations have been changed, the consequences must be systematically observed and adjustments made where necessary. This conclusion led the committee to recommend pilot studies, involving monitored operation of limited numbers of vehicles in actual commercial use, for evaluation of the consequences of changes in truck size and weight regulations (TRB 2002, 7–8).

12 Regarding the need for improvements in models, the committee emphasized the inadequacy of the method of estimating the effect of changes in truck weights on bridge costs. The method the study criticized is essentially the same as that of the 2016 USDOT study. The committee argued that the method is logically flawed and cannot produce cost estimates useful for guiding decisions. It recommended an alternative method (TRB 2002, 63–80). =========================================================================== BOX 5 TRB’s Regulation of Weights, Lengths, and Widths of Commercial Motor Vehicles: Conclusions and Recommendations Related to Data and Research (TRB 2002, 2–12) Conclusions (in part):  Appropriate objectives for size and weight regulations include to improve safety, to allow efficient commerce, to establish highway design parameters, to manage consumption of infrastructure  The methods of past studies have not produced satisfactory estimates of effect of changes in truck weights on bridge costs  Models and data will never be adequate to predict the outcomes of regulatory changes with high confidence  Research and monitoring needed to understand the relationship of truck characteristics to highway costs are not being conducted  Monitoring of compliance is too unsystematic to allow the costs of noncompliance to be estimated Recommendations (related to research):  The states and federal government should undertake systematic monitoring of truck traffic and truck costs to evaluate regulatory effectiveness  The states and federal government should undertake basic research on the relationship of truck characteristics to highway costs, including: – Evaluation of enforcement effectiveness – Evaluation of the relationship of truck performance to crash involvement – Risk-based evaluation of bridge costs – Freight transportation market research – Evaluation of costs and benefits of new infrastructure development and truck-only facilities – Pilot studies to test new vehicles ===========================================================================

13 Alternative Evaluation Methods All of the past studies described above were projections of performance and impacts of trucks operating under alternative size and weight limits based primarily on observations of the performance of more or less similar vehicles already in operation. (Some studies also have used simulation models of the effect of changing truck size and weight on pavement and bridges.) However, the new vehicles evaluated in the studies often had no close match among existing vehicles, or dimensionally similar vehicles were in use only in limited specialized freight operations. An evaluation approach that attempts to overcome this difficulty is to conduct trials to test the alternative vehicles in actual use. As noted above, the TRB committee that authored the report Regulation of Weights, Lengths, and Widths of Commercial Motor Vehicles concluded that projections of the outcomes of regulatory changes based solely on experience with vehicles currently in commercial use could never be highly reliable and recommended a program of pilot studies as a more definitive means to evaluate changes in truck size and weight regulations. The report outlined administrative arrangements for such a program (TRB 2002, 200–203). Trials on a range of scales have been conducted in the United States and other countries, from test track experiments to measure the dynamic properties of vehicles to the use of new vehicles in commercial freight operations that are subject to rigorous monitoring. FHWA, at the direction of Congress, has conducted monitoring and evaluation of the impacts of the 100,000 lb. gross weight trucks that Congress allowed to operate on interstate highways in Maine and Vermont (FHWA n.d.). In Canada, the Vehicle Weights and Dimensions Study (Roads and Transportation Association of Canada 1986), a joint project of the provincial and national governments and industry, recommended guidelines for uniform standards for transcontinental truck transportation on the basis of a research program of laboratory, track, and field testing and simulation to establish standards for vehicle stability and for pavement impact mitigation. In the Netherlands, longer and heavier vehicles were introduced in stages, beginning in 2001 with a small number of volunteer carriers operating a few trucks and then expanding to larger numbers of carriers and vehicles and finally to authorization for any carrier to apply for a permit to operate the larger

14 vehicles. Each stage has been subject to a rigorous program of monitoring of the infrastructure, safety, traffic, and freight transportation impacts, with decisions on expansion of the program contingent on the outcome of the monitoring. Monitoring continued after authorization of general use of the vehicles (Netherlands, Ministry for Infrastructure and Environment 2011). Germany authorized nationwide use of certain longer and heavier vehicles in 2017 following evaluation of the results of staged trials similar to the Netherlands approach. The trials evaluated the safety, traffic, infrastructure, and freight cost impacts of larger configurations with selected roads and carriers, preceding general authorization of the vehicles. The first stage of the trials, from 2012 to 2014, involved 43 vehicles operated by five commercial carriers. The subsequent stage involved 145 trucks and 56 companies. Trials are continuing for certain configurations not yet approved for general use. The trials have been conducted only with the agreement of the German states in which they occur. Evaluations were designed at the outset, with collection of baseline data and systematic monitoring (Knight 2017; Limbeck et al. 2017, 12–20). A research plan for evaluating changes in truck size and weight limits by means of pilot studies or trials would differ from a plan aimed solely at refining the traditional “pencil and paper” prospective evaluation method of past U.S. truck size and weight studies. Research would be needed to define the performance measures to be monitored, develop the data collection and analysis methods, determine the scale and participation rules of the trials, and develop the necessary administrative structure. Summary Observations General-purpose information systems and databases have been the primary information resource of past U.S. truck size and weight studies. These include state highway agencies’ traffic, crash, and vehicle weight databases and asset management systems, as well as national research and monitoring data systems such as the National Highway Traffic Safety Administration (NHTSA) crash databases, the Carload Waybill Sample, and the VIUS. Improvements in these information systems could improve

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TRB's Truck Size and Weight Limits Research Plan Committee has issued an interim letter report that explores the development of a research plan to reduce uncertainties in estimates of the impacts of changes in truck size and weight limits. The report summarizes the research recommendations of past truck size and weight limit studies, presents lists of candidate research problem statement topics, and identifies criteria for deciding the priority of topics for inclusion in the requested research plan, which will be presented in a final Academies report in fall 2018.

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