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Suggested Citation:"3 Conclusions." National Academies of Sciences, Engineering, and Medicine. 2019. Research to Support Evaluation of Truck Size and Weight Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25321.
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Suggested Citation:"3 Conclusions." National Academies of Sciences, Engineering, and Medicine. 2019. Research to Support Evaluation of Truck Size and Weight Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25321.
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Suggested Citation:"3 Conclusions." National Academies of Sciences, Engineering, and Medicine. 2019. Research to Support Evaluation of Truck Size and Weight Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25321.
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Suggested Citation:"3 Conclusions." National Academies of Sciences, Engineering, and Medicine. 2019. Research to Support Evaluation of Truck Size and Weight Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25321.
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Suggested Citation:"3 Conclusions." National Academies of Sciences, Engineering, and Medicine. 2019. Research to Support Evaluation of Truck Size and Weight Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25321.
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Suggested Citation:"3 Conclusions." National Academies of Sciences, Engineering, and Medicine. 2019. Research to Support Evaluation of Truck Size and Weight Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25321.
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Suggested Citation:"3 Conclusions." National Academies of Sciences, Engineering, and Medicine. 2019. Research to Support Evaluation of Truck Size and Weight Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25321.
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Suggested Citation:"3 Conclusions." National Academies of Sciences, Engineering, and Medicine. 2019. Research to Support Evaluation of Truck Size and Weight Regulations. Washington, DC: The National Academies Press. doi: 10.17226/25321.
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31 3 Conclusions The following conclusions about research needs and priorities are derived in part from the committee’s examination of the experience of the USDOT 2016 truck size and weight limits study (FHWA 2015a, 2016a) and the 2015 TRB committee review of the technical analysis of the USDOT study (TRB 2015). This recent experience reinforces conclusions of the 2002 TRB committee study Regulation of Weights, Lengths, and Widths of Commer- cial Motor Vehicles (TRB 2002), which are cited in the following section. Conclusions are presented on eight topics: • The value of research on truck size and weight regulations. • Limitations of impact projections. • The value of broadly applicable research. • The importance of general purpose data programs. • The need to match research to policy objectives. • The value of tests and trials in evaluations of truck size and weight limits. • Emerging technologies and truck size and weight regulations. • Organizational needs and options. VALUE OF RESEARCH ON TRUCK SIZE AND WEIGHT REGULATIONS A program of research and data collection targeting the most important gaps in understanding of impacts, together with improvements to exist­ ing data systems, would strengthen the federal and state governments’

32 EVALUATION OF TRUCK SIZE AND WEIGHT REGULATIONS capabilities to project the consequences of proposed changes in truck size and weight limits. Research could reveal important opportunities to im­ prove safety and productivity and to control highway construction and maintenance costs through better regulatory and management decisions. LIMITATIONS OF IMPACT PROJECTIONS Projections necessarily will be only approximate indicators of the range of possible outcomes of changes in the regulations. The 2002 TRB committee observed that “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” (TRB 2002, 3–4). A truck size and weight study should communicate this uncertainty to users of the study and identify uncertainties that are critical for decisions. The TRB committee that reviewed the USDOT 2016 study summarized techniques used in past studies for quantifying uncertainties, including sensitivity analysis to show how impact estimates are affected by statisti­ cal uncertainties in models and by study assumptions (TRB 2015, 14–15). Notwithstanding this uncertainty, legislators and government execu­ tives are regularly confronted with decisions on truck size and weight regulations and require technical guidance based on the best available infor­ mation. Past studies, while acknowledging the uncertainties, concluded that the evidence was sufficient to support recommendations. The 1964 federal study recommended specific changes in federal limits together with the in­ troduction of vehicle performance standards (DOC 1964, 2–6). The 1981 federal study by USDOT did not provide recommendations but reached firm conclusions about impacts of alternative limits that were a source of guidance for changes enacted in 1983. Earlier TRB committees (TRB 1990a, 1990b, 2002), consistent with their charges, recommended changes in limits, coupled with monitoring, enforcement, and user fee provisions. VALUE OF BROADLY APPLICABLE RESEARCH The data and analysis capabilities needed to project impacts of changes in limits are largely the same as the ones needed to manage the highway freight system under present limits—for bridge, pavement, and safety management; capacity planning; and setting of user fees. The projects in the roadmap that have the greatest potential value are projects that would improve truck size

CONCLUSIONS 33 and weight limit evaluations and also produce results with broader applica­ tions for highway management. For example, research on the determinants of bridge deck performance would have value for bridge life­cycle cost analysis, design, and asset man­ agement. Expanding the network of WIM sites would be valuable for asset management and capacity planning. In general, understanding the relation­ ship of truck traffic characteristics to highway agency costs and user costs is necessary for highway system management regardless of whether size and weight limits are changed. The potential for broad application will be important in justifying in­ vestment in the roadmap research and in recruiting support from the vari­ ous federal and state government agencies from which cooperation will be required to conduct the research. Research should be planned and designed with consideration of the full range of applications that would have the greatest long­term value. IMPORTANCE OF GENERAL PURPOSE DATA PROGRAMS Ongoing data programs maintained by the state highway agencies for man­ agement purposes and by the federal government for performance moni­ toring and research are the basis of understanding of truck impacts and have been among the principal resources in past evaluations of proposed changes in limits. These include state highway agencies’ bridge and pave­ ment management systems and traffic, crash, and vehicle weight databases; USDOT’s motor vehicle crash and motor carrier enforcement data systems, Long­Term Infrastructure Performance Programs, and National Bridge In­ ventory; the Surface Transportation Board’s Carload Waybill Sample; and the Census Bureau’s Commodity Flow Survey and Vehicle Inventory and Use Survey. Strengthening these information systems would allow improved highway management today as well as improved understanding of the costs and benefits of changes in truck size and weight limits. Evaluation of truck size and weight regulations requires data on pave­ ment and bridge condition, safety, and truck weights and truck traffic volume on roads owned and maintained by county, city, and other local governments. Programs to collect infrastructure and traffic data on local roads are generally weak. Local roads carry about 15 percent of U.S. com­ bination truck­miles of travel, but include nearly 80 percent of U.S. road mileage (FHWA 2017a, Tables HM­16, VM­1). Bridges and pavements on local roads typically are of lighter construction than those on major roads, and local governments often have fewer resources for maintenance and enforcement than state governments. Therefore, many local roads are more susceptible than major roads to effects of changes in truck sizes and weights.

34 EVALUATION OF TRUCK SIZE AND WEIGHT REGULATIONS NEED TO MATCH RESEARCH TO POLICY OBJECTIVES The TRB 2002 and 2015 committees recommended that the objective of evaluations of truck size and weight limits should be to identify policies that would increase public benefits through improved operation of the highway freight transportation system: The best way to control the costs of accommodating existing and future truck traffic is by coordinating practices in all areas of highway manage­ ment: design and maintenance of pavement and bridges; highway user regulations; and highway user fees…. Whenever Congress contemplates changing policy in any one of these three areas in the federal aid highway program, it should at the same time consider the need for complementary changes in the other two. (TRB 2002, 3) The goal of research should be development of comprehensive strate­ gies 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 evaluations of comprehensive policy options rather than evaluations of alternative truck configurations. (TRB 2015, 4) The state, local, and federal governments are together responsible for all aspects of the operation of the highway system, including design, asset management, safety regulation, size and weight regulations, user fees, and enforcement. The impact of a change in size and weight limits depends on practices in each of these areas. As the description in Chapter 1 of the structure of truck size and weight studies noted, research will be required to develop methods that can be used in future studies to evaluate coordinated policies, including the effects of user fees, enforcement, asset management, and vehicle performance standards on truck traffic costs. A USDOT study conducted at the direction of Congress must fulfill the specific requirements of Congress, which may include narrowly defined regulatory questions such as the impact of exempting particular routes in one state from a federal limit. However, a federal truck size and weight study intended to be comprehensive, that is, to provide general policy guid­ ance, will be most useful if it is organized as an evaluation of coordinated policies that seeks to identify opportunities for increasing public benefits. VALUE OF TESTS AND TRIALS IN EVALUATIONS OF TRUCK SIZE AND WEIGHT LIMITS Road trials and vehicle testing would be useful components of evaluations of proposed changes in limits. The new vehicles that come into use after a

CONCLUSIONS 35 nationwide change in regulations are likely to differ from any dimension­ ally similar vehicles in use before the change with respect to loads, routes, equipment characteristics, and operator characteristics. For example, since federal law legalized use of twin 28­ft trailers in 1983, the predominant users of this configuration have been nationwide parcel and less­than­ truckload carriers, but most prior use had been intrastate carriage of agri­ cultural products (TRB 1986, 75–80). Therefore, the pre­1983 experience had limited value for predicting the performance of post­1983 twin trailers. The 1983 changes in federal regulations also led to nationwide use of the 53­ft single­trailer combination, with which there had been practically no previous experience. The TRB committee that authored the report Regulation of Weights, Lengths, and Widths of Commercial Motor Vehicles recommended a pro­ gram of road trials (termed pilot studies in the report), involving selected carriers and a limited network of roads, as a means to evaluate changes in truck size and weight regulations to supplement the information avail­ able from historical experience (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 systematic monitoring. Track testing and simulation modeling can guide the specification of standards to assure acceptable performance of new vehicles with respect to stability, control, and pavement impact. Systemati­ cally conducted road trials have been used to provide a realistic check on motor carrier use of new vehicles and infrastructure interactions. A road trial would provide information on crash characteristics for new vehicle types, although differences in crash rates among vehicle types would be observable only in large­scale trials of long duration. A trial would be undertaken with safeguards. Vehicles would be evalu­ ated for stability before the trial with track testing and engineering analysis. Drivers and participating carriers would be required to meet standards for past safe operation. Roads designated for the trial would be compatible with the characteristics of the trucks. The trials would be subject to moni­ toring to detect incipient problems. Such trials would be an improvement in safe practice in comparison with present practice, under which changes in limits and the issuance of permits for oversize and overweight vehicles usually occur without systematic monitoring of consequences. EMERGING TECHNOLOGIES AND TRUCK SIZE AND WEIGHT REGULATIONS Technological developments in the motor vehicle and trucking industries will influence the consequences of changes in size and weight limits. The

36 EVALUATION OF TRUCK SIZE AND WEIGHT REGULATIONS following are some of the technologies in truck transportation and trucking regulation that may become more important over the next 10 to 15 years and the truck costs that they will affect: • Platooning: truck freight cost, safety, and pavement and bridge costs. • Advanced driver assistance systems, including electronic stability control and collision avoidance: crash risk (in particular, for multi­ trailer combinations). • Automated driving systems: truck freight cost, crash risk, and pave­ ment and bridge costs. • Active suspensions: pavement and bridge costs (by controlling dy­ namic loading). • Truck telematics, including vehicle tracking, electronic logging, safety analytics, and onboard mass monitoring: enforcement cost and effectiveness and truck freight cost. • Electrification: truck freight cost and pollution cost. Some consequences of these technologies are clearly relevant to government decisions about truck size and weight regulation. For example, stability control and other forms of automation might reduce any differences in crash risk related to vehicle configuration. Technological advances that substantially reduce truck freight costs will affect modal competition and the volume of truck freight. The research problem statements include research tasks to examine the influence of some of these technologies, including use of information technologies in enforcement (problem statements E.3 and E.4) and the ef­ fect of platooning on pavement and bridge costs (problem statements P.3 and B.7). Research to develop procedures to evaluate the performance of vehicles with track testing (problem statement S.5) will provide information on the potential value of electronic stability control, active suspensions, and collision avoidance systems for mitigating the costs of truck traffic. For technologies still in an early stage of development (for example, electrifica­ tion and full automation of large trucks), it will be necessary to monitor progress until the course of the technology is clearer and specific research needs become evident. ORGANIZATIONAL NEEDS AND OPTIONS USDOT should consider the research topics proposed in this report as components of its coordinated research plan to meet the needs of its policy, freight, infrastructure, and safety programs. If USDOT determines that

CONCLUSIONS 37 improved projections of particular categories of impacts are necessary, then the roadmap projects that address these impacts can guide the research. The committee was not charged with recommending the internal organiza tion of USDOT research, but presumably most federal research projects in the roadmap would involve collaboration among FHWA offices (includ ing the freight, research, infrastructure, policy, and safety offices) or with other USDOT agencies (National Highway Traffic Safety Administra­ tion, Federal Railroad Administration, or the Federal Motor Carrier Safety Administra tion). FHWA could submit projects that would have products useful to the states for consideration by NCHRP. Projects could also be organized through FHWA’s Transportation Pooled Fund Program as joint projects of FHWA, other federal agencies, states, and other interested par­ ties. Certain safety projects could involve industry participation and in­kind contributions. To provide an organizational home for research in the roadmap, USDOT may wish to designate an office responsible for coordinating the program of all research projects that are expected to contribute to improv­ ing capabilities for evaluating changes in truck size and weight limits. The coordinator would be responsible for maintaining communication among all the parties contributing to the research program, including sponsors, highway agencies, and investigators for the various research projects; iden­ tifying specific coordination needs (for example, data and modeling capabil­ ity requirements); and setting milestones and tracking progress toward the program’s objectives.

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TRB's Truck Size and Weight Limits Research Plan Committee has issued its second and final report, Research to Support Evaluation of Truck Size and Weight Regulations, to the U.S. Department of Transportation. The report presents a research plan to reduce the major sources of uncertainty in projections of the consequences of proposed changes in truck size and weight limits. The report defines a program of 27 coordinated research projects in six areas.

The committee acknowledges that improvements in models for projecting impacts of changes in truck size and weight limits, while necessary, will not guarantee the success of future truck size and weight policy studies. Future studies will be useful as guides for decisions only if policy objectives and practical policy options are clearly defined, the analysis is logically structured to reveal the most promising policies, and uncertainties are properly characterized.

The committee issued its first report in April 2018, which summarized the research recommendations of past truck size and weight limit studies and identified criteria for deciding the priority of topics for inclusion in the research plan.

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