Review of U.S. Department of Transportation Truck Size and Weight Study - Second Report: Review of USDOT Technical Reports (2015)

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SUMMARY The U.S. Department of Transportation (USDOT) asked the Transportation Research Board to convene a committee to review the study of truck size and weight limits that the 2012 surface transportation authorization act requires USDOT to carry out. The first report of the committee (TRB 2014) reviewed preliminary products of the study. This final report is the committee’s review of the USDOT study’s technical reports, which present estimates of five categories of impacts of changes in federal truck size and weight limits: effects on bridges, pavements, shares of total freight traffic carried by trucks and other freight modes, safety, and enforcement of truck regulations. In its review, the committee considered how the USDOT study addresses the questions identified by Congress and the appropriateness of the methods and data used to produce the estimates. The committee’s recommendations propose actions suggested by the experience of the USDOT study to increase the value of any future truck size and weight studies. Responsiveness to the Questions Identified by Congress The USDOT report specifies how the study attempted to address the requirements of the legislative charge and acknowledges gaps in its ability to estimate impacts of alternative configurations. However, a more comprehensive and useful response would have been possible within the resources of the study. Areas in which the study fell short of the requirements are described below. Lack of a Summary Evaluation The USDOT report lacks a consistent and complete quantitative summary of the evaluations of the alternative configuration scenarios. Important categories of costs are not estimated, measures of the various impacts are incommensurate, and assessments of the uncertainty of estimates are missing or inaccurate. Consequently, the information presented does not enable the reader to form a coherent picture

2 of the likely impacts of allowing alternative configurations or of the degree of confidence to place in the predictions of impacts. At the least, the report could have provided a framework for understanding all the costs and benefits. A comprehensive list of the categories of costs and benefits, the features of the hypothesized regulatory change that influence each category, the direction of change, and the categories that are likely to be critical to the evaluation all can be identified from results of the present and past studies. Costs that were not estimated in the USDOT study include the following major categories, as well as others of probably smaller magnitude:  Infrastructure costs on roads not part of the Interstate system or National Network,  Expected or likely bridge structural costs,  User costs of bridge replacements and retrofits and of bridge weight restrictions, and  Aggregate crash and casualty frequency and associated costs. Units of measure in which the impacts estimates are presented are inconsistent; therefore, the report cannot support the process of weighing costs, benefits, and trade-offs of alternative courses of action that regulatory decisions require. Changes in logistics, congestion, and enforcement costs are reported in annual dollars; bridge costs are reported as an initial capital expenditure; pavement costs are reported as the percentage change in present value of all future costs; and energy and pollution impacts are expressed in physical units. Evaluation of Consequences of Grandfather Exemptions The legislative study charge appears to call for USDOT to assess the costs and benefits of impacts of the grandfather and other exemptions in federal size and weight regulations on infrastructure, safety, and state

3 finances in each state where the exemptions are in effect. The study does not provide such an overall assessment. Methods and Data Chapters 3 through 7 present conclusions with regard to the methods and data used in the estimates of each category of impact in the USDOT study. Highlights of those conclusions include the following:  The procedure for selecting the sample of bridges used in the bridge analysis may have introduced bias. The sample was selected judgmentally from among bridges for which the necessary input data were already available. The method of defining the representative pavements analyzed also gives rise to concern about possible bias.  In the alternative configuration scenarios, the estimates of diversion of freight from rail to truck and of the redistribution of freight among truck configurations use a synthetic database of shipments in which shipment size and other characteristics are assumed. The effect of the assumptions on the accuracy of the mode share projections is unknown.  The estimated logistics cost savings per vehicle mile of truck traffic reduction are much larger than in earlier studies for the alternative configuration scenarios involving heavier tractor-semitrailers. Confidence in the estimates could have been strengthened by accounting for such differences.  The estimates of actual vehicle miles of travel by each truck configuration (which affect the estimates of infrastructure and safety impacts of alternative configurations) are derived from data collected by the states from weigh-in-motion (WIM) devices. Interpretation of WIM data is difficult. The USDOT report does not indicate whether any tests of the estimates’ accuracy were carried out.  The comparisons of alternative configuration and control vehicle crash rates do not consider some factors that influence safety performance, including driver characteristics, company management

4 practices, and the temporal distribution of travel. The populations of the alternative configurations are likely to differ from the control vehicles in some of these factors.  In the vehicle stability simulations, the rearward amplification of triple-trailer configurations in the avoidance maneuver was found to be no different from that of doubles. Earlier studies found the rearward amplification of triples to be substantially more severe than that of doubles. Examination of the source of differences with past results would have enhanced the credibility of the USDOT study. Recommendations USDOT should promote improvement of state information systems aimed at monitoring the impact of existing truck traffic on highway performance. Improvements in information systems would support highway agencies’ efforts to manage impacts and would have the secondary benefit of allowing more credible projections of the effects of changes in truck regulations. The most critical needs are for better understanding of how truck traffic affects crash risks and of how it affects bridge-related costs. USDOT and state analyses of truck size and weight 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, monitoring, and inspection practices; enforcement of regulations; and design of permit and fee systems. The goal should be development of comprehensive strategies for reducing the public costs and increasing the benefits of highway freight transportation. Chapters 3 through 7 present recommendations for improving estimates in each of the impact categories in any future truck size and weight study. The following are highlights of the recommendations:  Bridge cost estimates in any future study should be based on explicit assumptions about state highway agency responses to changes in truck traffic. Projections of probable state responses and determination of economically optimal responses both would be useful.

5  The analysis of pavement and bridge impacts in any future USDOT truck size and weight study should include estimates of costs derived from evaluations of scientifically designed samples of actual pavements and actual bridges selected from the entire U.S. road system.  USDOT should undertake research to improve understanding of the behavioral factors that influence freight demand, analytical techniques to depict freight markets as they are affected by public policy, and data required for freight market analysis. Research should develop and test three methods of predicting mode choice: disaggregate models, aggregate econometric models, and expert opinion.  USDOT should continue to support three potentially valuable areas of research and data development begun in the present study: - Development of data systems in cooperation with the states to monitor the safety performance of truck configurations. Refinement and validation of WIM-derived vehicle distributions would improve exposure data for estimating crash rates. - Research to understand the relationship of crash frequency on a road to the traffic volume and mix of vehicle types on the road. - Analysis of the relationship between weight enforcement effort and frequency of violations. Knowledge of this relationship could lead to improvement in the cost-effectiveness of enforcement. Reference Abbreviation TRB Transportation Research Board TRB. 2014. Review of U.S. Department of Transportation Truck Size and Weight Study: First Report: Review of Desk Scans. March 31. http://onlinepubs.trb.org/onlinepubs/sr/TS&WDeskScans.pdf.