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Suggested Citation:"1 Introduction." 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:"1 Introduction." 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:"1 Introduction." 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:"1 Introduction." 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:"1 Introduction." 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:"1 Introduction." 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:"1 Introduction." 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:"1 Introduction." 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:"1 Introduction." 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:"1 Introduction." 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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5 1 Introduction USDOT delivered to Congress the final report of its Comprehensive Truck Size and Weight Limits Study (FHWA 2016a) in 2016, according to the requirements of Section 32801 of the Moving Ahead for Progress in the 21st Century Act (MAP­21) of 2012. The act called for a study to compare the impacts of truck traffic operating under present federal regulations with the impacts if truck configurations exceeding present size and weight limits were allowed to operate, with respect to safety, infrastructure, cost re­ sponsibilities, fuel efficiency, freight transportation costs, the environment, truck traffic volumes, and shares of freight traffic carried by trucks and other freight modes. The act also required an evaluation of the frequency of violations of federal truck size and weight regulations and the cost and effectiveness of enforcement. The 2016 study was the most recent of a series of federal evaluations of truck size and weight regulations conducted over the past several decades (see Box 1­1). In its report to Congress, USDOT observed that “the analytical work revealed very significant data limitations that severely hampered efforts to conclusively study the effects of the size and weight of various truck configurations” (FHWA 2016a, 17) and recommended that a program of research be undertaken to overcome these limitations (FHWA 2016a, 21): “To make a genuine, measurable improvement in the knowledge needed for these study areas, a more robust study effort should start with the design of a research program that can identify the areas, mechanisms, and practices needed to establish new data sets and models to advance the state of practice.”

6 EVALUATION OF TRUCK SIZE AND WEIGHT REGULATIONS BOX 1-1 Federal Truck Size and Weight Studies, 1941–2016 Interstate Commerce Commission (1941): Federal Regulation of the Sizes and Weights of Motor Vehicles U.S. Department of Commerce (1964): Maximum Desirable Dimensions and Weights of Vehicles Operated on the Federal-aid Systems USDOT (1968): Economics of the Maximum Limits of Motor Vehicle Dimensions and Weights USDOT (1981): An Investigation of Truck Size and Weight Limits USDOT (2000a): Comprehensive Truck Size and Weight Study USDOT (2004): Western Uniformity Scenario Analysis FHWA (2016a): Comprehensive Truck Size and Weight Limits Study In 2017, the FHWA Office of Freight Management and Operations asked TRB to develop a plan for a research program as recommended in the 2016 USDOT final report. In response, TRB organized the Truck Size and Weight Limits Research Plan Committee, which was charged with the following task: This project will develop and recommend a research roadmap to address gaps and uncertainties in estimating the impacts of changes in truck size and weight limits. Specific research projects, estimated costs, and time­ lines will be recommended in the areas of safety, compliance/enforcement, modal shift, bridges, and pavements. The recommendations will include ef­ ficient means of collecting data essential to estimating the impacts of larger and heavier trucks in these five areas on national, state, and local roads. The first report of the committee (TRB 2018) summarized research rec­ ommendations of past truck size and weight limit studies and listed research topics under consideration for inclusion in the committee’s research plan in each of the five categories of impact identified in the task statement (safety, enforcement, modal shift, bridges, and pavements) as well as research top­ ics on methods to evaluate alternative truck size and weight regulatory structures. The first report also discussed the criteria that the committee would take into account in deciding the priority of topics for inclusion in its research plan. This second report presents the committee’s research plan (that is, the research roadmap to which the task statement refers). The committee has defined a program of coordinated research projects, aimed at reducing the major sources of uncertainty in past projections of the consequences of proposed changes in truck size and weight limits. For each project, the

INTRODUCTION 7 report provides a problem statement identifying the product, relationship to the overall problem of evaluating truck size and weight regulations, possible research approaches, anticipated duration and cost, and necessary participants in the research. The research program is selective; it includes projects on the catego­ ries of impact identified in the Statement of Task and certain additional topics that the committee concluded require attention, but does not in­ clude research on all significant categories of impact of changes in the limits. In particular, research projects on environmental, energy, and traffic congestion impacts have not been included. These impacts may be impor­ tant considerations in future decisions on the regulations. However, their estimates have not been critical sources of uncertainty in past size and weight studies because the uncertainty in projections of environmental, energy, and congestion impacts arises primarily from uncertainty in the projected change in truck traffic volume caused by a change in regulations. Research to develop improved methods of projecting truck traffic changes is included in the research roadmap. A 1996 TRB committee report dem­ onstrated methods for estimating social costs of freight transportation and illustrated the relative magnitudes of public and private costs in selected cases (TRB 1996). Even major improvements in models for projecting infrastructure, safety, and freight cost consequences of changes in limits will not guaran­ tee 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 character­ ized. The recommendations of the TRB committee that reviewed the tech­ nical analysis of the 2016 USDOT size and weight study emphasized not only the importance of improving impact models, but also the importance of providing a logical structure that clarifies choices for decision makers. For example, the committee noted the need to present all cost and benefit estimates in consistent, comparable units of measure; the need to estimate systemwide safety impacts (the net effect of changes in truck characteristics and truck traffic volume); and the need to evaluate alternative regulations and not simply alternative vehicles (TRB 2015, 10–21). Designing the most useful structure for any future comprehensive truck size and weight policy study (including the definitions of objectives, policy alternatives, and decision rules) is itself a problem requiring research. The ideal structure would be as an economic optimization problem: the analy­ sis would identify the range of practical options for government actions, including size and weight limits and related road management practices (user fees, enforcement, road design, and asset management), project com­ prehensive public and private costs and benefits, and select the package of

8 EVALUATION OF TRUCK SIZE AND WEIGHT REGULATIONS policies that promised the greatest net benefit for the public. The committee has included research topics to develop an analysis framework for truck size and weight policy studies in the roadmap. SOURCES FOR THE ROADMAP To identify the major sources of uncertainties in projections of impacts of changing truck size and weight limits, the committee reviewed the results of the USDOT truck size and weight studies of 2016, 2000, and 1981 and the conclusions these studies reached about deficiencies in data and models available for the analyses. The 2016 USDOT study report identifies the de­ ficiencies in data and models that the study encountered and recommends numerous improvements (FHWA 2016a, 21–25). The committee also identified research requirements arising from recent developments not considered in the 2016 USDOT study or in the earlier studies, in particular, the implications of truck platooning (operation of two or more trucks in a convoy with close spacing maintained by an advanced driver assistance system) and other information technology advances ap­ plied to truck operations that may cause future truck performance and patterns of use to diverge from historical experience. Sources on the state of knowledge of modeling impacts and on possible research approaches included the research undertaken by USDOT in sup­ port of its 2016 study; research recommendations of past TRB committees, including the committee that conducted a review of the technical analyses of the USDOT 2016 study (TRB 2015); and a series of public webinars at which experts invited by the committee offered comments on research priorities and methods in each of the impact areas. The webinar programs appear in Appendix B. The 2002 report of the TRB Committee for the Study of the Regulation of Weights, Lengths, and Widths of Commercial Motor Vehicles (TRB 2002) was an important resource for the present committee. The 2002 report was prepared in response to a congressional directive for a study of the federal regulation of truck sizes and weights and for recommendations on revisions. Its conclusions were based on a detailed review and assessment of the major prior studies of size and weight limits by the federal government, TRB com­ mittees, and others. The 2002 committee’s conclusions about uncertainties and errors in past evaluations, the method of estimating effects of changes in truck size and weight limits on bridge costs, the design of trials to evaluate new truck configurations, and the appropriate structure and objectives of truck size and weight studies are cited in later sections of this report. The present committee’s first report summarizes recommendations re­ lated to research and data requirements from the USDOT studies and from past TRB committee evaluations of truck size and weight limits (TRB 2018,

INTRODUCTION 9 5–15). It also identifies candidate research topics for the roadmap, compiled from the sources previously described, in each of the five impact areas of pavement, bridges, safety, enforcement, and mode choice, together with a list of cross­cutting topics (TRB 2018, 15–24). The first report also describes six criteria that the committee has con­ sidered in setting priorities among the inventory of research and data needs and in defining the appropriate roles of USDOT and other possible partici­ pants in research and data collection (TRB 2018, 25–29): • Relative magnitudes of the potential cost changes caused by a change in limits. • Degree of uncertainty in present estimates. • Likelihood that research could make progress. • Public and interest group concerns. • Potential value of research results for general highway management applications. • Assumed objectives of the regulatory changes under consideration. Each research problem statement in this report includes an examination of the priority of the topic, with reference to these criteria. STRUCTURE OF TRUCK SIZE AND WEIGHT LIMIT STUDIES The committee recognized that the research program must be designed to fit the needs of the intended applications. Therefore, it examined the methods of past truck size and weight limits policy studies to understand the infor­ mation requirements of these studies. Nearly all past U.S. studies followed a similar conceptual framework for evaluating proposed changes in size and weight limits. The steps in this conventional method (see Figure 1­1) are as follows: 1. Specify a set of alternative regulatory scenarios (size and weight limits and related regulations such as route restrictions). 2. Project truck traffic volume and composition in each scenario. 3. Project changes in costs affected by the change in limits, including highway agency costs to construct and maintain roads and bridges; freight shipper and carrier costs; highway user costs, including congestion and crash risk; and other costs to the public such as pollution. 4. Assess certain other collateral effects of the change in limits, includ­ ing rail industry impact and highway agency budget impact. 5. Recommend any changes in limits that the evaluation indicates would be beneficial, considering costs, benefits, practical constraints,

10 FI G U R E 1 -1 S tr uc tu re o f a tr uc k si ze a nd w ei gh t po lic y ev al ua ti on . Ch an ge in pa ve m en t c os ts Ch an ge in b rid ge co st s Ch an ge in sa fe ty co st s M od e an d tr uc k tr af fic v ol um es : Fr ei gh t t ra ffi c vo lu m e by m od e; Tr uc k tr af fic b y co nf ig ur at io n, a xl e an d gr os s w ei gh t, ro ut e En fo rc em en t im pa ct Tr uc k siz e an d w ei gh t re gu la tio ns Tr uc k siz e an d w ei gh t en fo rc em en t O th er c on di tio ns (r eg ul at or y, us er ta x, te ch ni ca l, m ar ke t) Fr ei gh t s hi pp er a nd c ar rie r re sp on se Sa fe ty Sa fe ty O th er im pa ct s: tr af fic op er at io ns , po llu tio n, en er gy , r eg io na l, ra il in du st ry ... Ch an ge in sh ip pe r c os t o f fr ei gh t tr an sp or ta tio n Hi gh w ay a ge nc y pr ac tic es : pa ve m en t m an ag em en t an d de sig n Hi gh w ay a ge nc y pr ac tic es : br id ge m an ag em en t a nd de sig n Ag en cy p ra ct ic es : en fo rc em en t, sa fe ty m an ag em en t, an d de sig n

INTRODUCTION 11 and uncertainties. Some studies present results of the comparative analysis of regulatory alternatives without recommendations. The committee’s task statement is consistent with the needs of a truck size and weight study that follows this framework, that is, a prospective study that attempts to forecast changes in traffic and in costs from a change in limits. The five impact areas in the task statement are elements of the framework: mode choice, safety, pavement, bridges, and enforcement. The TRB Commercial Motor Vehicles committee (TRB 2002, 41–47) rec­ ommended two fundamental modifications to this conventional framework: • Any future truck size and weight study should be structured as an evaluation of alternative policies for achieving a specified objective, rather than as an evaluation of alternative vehicles. The alternative policies considered would include not only changes in limits, but also coordinated changes in other highway management practices that affect the performance of highway freight transportation. • In recognition of the unavoidable uncertainties in forecasts of the consequences of new regulations, evaluation of new regulations should include systematic monitoring of consequences whenever regulations are changed. The steps in such an evaluation would be the following: 1. Define the specific policy objective that changes in regulations and practices would be intended to achieve in terms of increased public benefits from the highway freight transportation system. 2. Specify an initial package of policies aimed at the objective, includ­ ing changes in truck size and weight limits and related policies, which could include changes in safety regulations, user fees, asset management, pavement and bridge design and rehabilitation meth­ ods, and enforcement. 3. Project the private­sector response and public costs and benefits of the policy package according to the conventional method shown in Figure 1­1. 4. Compare the projected outcome with the objective. If the outcome falls short, revise the policy package to try to overcome the obsta­ cles that the evaluation has revealed and repeat the evaluation with the revised policy package. Iterate to identify the best opportunities for achieving the objective. 5. If regulatory changes are adopted, systematically monitor the con­ sequences and identify adjustments to regulations and practices needed to bring the outcome closer to the objective.

12 EVALUATION OF TRUCK SIZE AND WEIGHT REGULATIONS Past truck size and weight studies acknowledged the potential value of coordinating size and weight regulations with other highway manage­ ment practices to achieve an objective of improved system performance. For example: • The 1981 and 2000 USDOT truck size and weight studies (US­ DOT 1981, 2000a) were conducted in conjunction with highway cost allocation studies, in recognition of the need to align user fees with size and weight limits. The USDOT studies did not project how changes in fees would affect the consequences of changing the limits, but such alignment could strongly influence truck operators’ equipment choices (Small et al. 1989, 55–56). • The TRB committee study of the Turner Proposal (TRB 1990b) (a proposal to allow operation of higher gross weight trucks with lower maximum axle weight limits) sought changes in size and weight limits and other practices to attain a defined performance objective, the simultaneous reduction of shippers’ freight costs and infrastructure costs. The committee could not identify such a win–win outcome, but proposed a coordinated package of size and weight, safety, user fee, enforcement, and asset management policies aimed at increasing public benefits. • In the 1981 USDOT study, “Scenario K” was a similar attempt to specify limits that would increase freight productivity and reduce infrastructure costs (USDOT 1981, II­7–II­8). • The 1964 U.S. Department of Commerce (DOC) study recom­ mended changes in limits coupled with the imposition of per­ formance standards for engine power, braking, and the linkages between combination units (DOC 1964, 5). As hypothetical examples, the objective of a future truck size and weight study might be defined as designing a package of truck user fees and size and weight limits that would allow increased freight productivity and provide the revenue needed for infrastructure upgrades to accommodate more productive vehicles, or as designing a package that reduced infrastruc­ ture costs without degrading freight productivity or safety. Such proposals start with the premise that present regulations and practices are far from the optimum and can be improved. With respect to the committee’s task, the framework that future truck size and weight studies will adopt is relevant because it dictates research needs. If a framework of seeking policies that increase public benefits is adopted, models capable of evaluating coordinated policies will be needed, including

INTRODUCTION 13 • Models of mode and vehicle choice in the private sector that are able to represent the effect of alternative highway user fee and tax structures on the use of existing and new configurations. • Methods to project the effect of alternative enforcement practices on weight distributions. • Models of pavement­ and bridge­related costs that are able to represent the consequences of alternative highway agency asset management and weight enforcement practices. • A method of projecting safety impact that is capable of represent­ ing the effect of vehicle performance standards on crash risk. With few exceptions, past truck size and weight studies have not developed methods for these kinds of analyses. OUTLINE OF THE REPORT Chapter 2 is a summary of the roadmap. Chapter 3 presents conclusions of the committee about research needs, priorities, and the organization of future research. Appendix A contains research problem statements for the projects in the roadmap in the five impact areas of pavements, bridges, safety, enforcement, and mode choice as well as cross­cutting topics (topics relevant to all impact categories). The research problem statements in each impact area are preceded by a discussion of the motivation for the research, with respect to deficiencies of past estimates and the importance of the impact to the overall evaluation of alternative regulations. Appendix B contains the programs of the public webinars organized by the committee.

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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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