Truck Weight Limits

TRB's National Cooperative Highway Research Program (NCHRP) Report 671: Review of Canadian Experience with the Regulation of Large Commercial Motor Vehicles examines the process used in Canada to harmonize heavy truck size and weight regulations across the country. The report provides insights on how lessons learned from the Canadian experience might be applied in the United States.

To help assess proposals for further changes in federal truck weight limits, Congress requested this study through Section 158 of the Surface Transportation and Uniform Relocation Assistance Act of 1987. To conduct the study, the National Research Council convened a special Transportation Research Board committee with experts in pavements, bridges, highway safety, freight transportation economics, motor vehicle design, highway administration, motor carrier operations, and enforcement of motor vehicle regulations. The study focused on four issues identified in the study request that involve potential changes to federal weight limits for Interstate highways: (1) Elimination of existing grandfather provisions; (2) Alternative methods for determining gross vehicle weight and axle loadings; (3) Adequacy of the current federal bridge formula; and (4) Treatment of specialized hauling vehicles--garbage trucks, dump trucks, and other trucks with short wheel bases that have difficulty complying with the current federal bridge formula. For each of these issues, the study committee estimated the nationwide effects of changes in federal limits proposed by the trucking industry, highway agencies, and other groups. Projections of heavy-truck miles by type of truck, region of the country, highway functional class, and operating weight were developed for a base case and alternative truck weight regulatory scenarios. These projections were then used to estimate impacts on truck costs, pavements, bridges, and safety.

TRB's Special Report 328: 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.