Regulating Weights, Lengths, and Widths of Commercial Motor Vehicles

TRB Special Report 267 - Regulation of Weights, Lengths, and Widths of Commercial Motor Vehicles recommends the creation of an independent public organization to evaluate the effects of truck traffic, pilot studies of new truck designs, and a change in federal law authorizing states to issue permits for operation of larger trucks on the Interstates.

In 1991, Congress placed a freeze on maximum truck weights and dimensions. Some safety groups were protesting against the safety implications of increased truck size and weight, and the railroads were objecting to the introduction of vehicles they deemed to have an unfair advantage. Railroads, unlike trucking firms, must pay for the capital costs of their infrastructure. The railroads contend that large trucks do not pay sufficient taxes to compensate for the highway damage they cause and the environmental costs they generate. Although Congress apparently hoped it had placed a cap on maximum truck dimensions in 1991, such has not proven to be the case.

Carriers operating under specific conditions have been able to seek and obtain special exceptions from the federal freeze by appealing directly to Congress (without any formal review of the possible consequences), thereby encouraging additional firms to seek similar exceptions. In the Transportation Equity Act for the 21st Century, Congress requested a TRB study to review federal policies on commercial vehicle dimensions.

The committee that undertook the study that resulted in Special Report 267 found that regulatory analyses of the benefits and costs of changes in truck dimensions are hampered by a lack of information. Regulatory decisions on such matters will always entail a degree of risk and uncertainty, but the degree of uncertainty surrounding truck issues is uunusually high and unnecessary. The committee concluded that the uncertainty could be alleviated if procedures were established for carrying out a program oof basic and applied research, and if evaluation and monitoring were permanent components of the administration of trucking regulations.

The committee recommended immediate changes in federal regulations that would allow for a federally supervised permit program. The program would permit the operation of vehicles heavier than would normally be allowed, provided that the changes applied only to vehicles with a maximum weight of 90,000 pounds, double trailer configurations with each trailer up to 33 feet, and an overall weight limit governed by the federal bridge formula. Moreover, enforcement of trucks operating under such a program should be strengthened, and the permits should require that users pay the costs they occasion. States should be free to choose whether to participate in the permit program. Those that elected to do so would be required to have in place a program of bridge management, safety monitoring, enforcement, and cost recovery, overseen by the federal government.

The fundamental problem involved in evaluating proposals for changes in truck dimensions is that their effects can often only be estimated or modeled. The data available for estimating safety consequences in particular are inadequate and probably always will be. Thus, the committee that conducted this study concluded that the resulting analyses usually involve a high degree of uncertainty. What is needed is some way to evaluate potential changes through limited and carefully controlled trials, much as proposed new drugs are tested before being allowed in widespread use.

The committee recommended that a new independent entity be created to work with private industry in evaluating new concepts and recommending changes to regulatory agencies. Limited pilot tests would be required, which would need to be carefully designed to avoid undue risks and ensure proper evaluation. Special vehicles could be allowed to operate under carefully controlled circumstances, just as oversize and overweight vehicles are allowed to operate under special permits in many states. Changes in federal laws and regulations would be required to allow states to issue such permits on an expanded network of highways, under the condition that a rigorous program of monitoring and evaluation be instituted.