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Summer/Fall 2002 Vol. 2 No. 2



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Tractor-trailer ©Digital Stock Pushing
the Limits


Are Trucks Too Big
and Heavy?

While driving down a local highway, have you ever found yourself doing a double take when a tractor-trailer zooms past? The trucks seem larger than the ones on the interstate. It's no illusion. They might very well be.

Given current federal size limits, larger trucks sometimes have to avoid interstate highways and use secondary roads where accidents are more likely to happen and maintenance costs are higher.

The federal government first placed limits on truck size and weight in 1956, as part of the legislation that created the federal highway program. Since then, the regulations have only been significantly revised twice. In 1991, Congress passed a law as a safety measure that prohibits states from expanding the use of heavier double and triple trailers.

But a new report from the Transportation Research Board recommends that the government should authorize states to allow trucks exceeding present federal limits to operate on interstate highways, provided that impacts on safety and road-maintenance costs are monitored.

The standard tractor-trailer has five axles, and the current federal limit is 80,000 pounds. States should be allowed to issue permits for the operation of six-axle tractor-trailers weighing up to 90,000 pounds, the report says. Increasing the length of the truck reduces shipping costs moderately, and lowering the weight-per-axle ratio cuts down on pavement wear and tear. But an overall increase in the total weight of trucks also results in higher costs for bridge construction and highway maintenance.

The committee that wrote the report recommends Congress should charter a new organization to oversee implementation of federal truck-size regulations and evaluate their results, carry out pilot studies and research to determine the impact of trucks on highways, and recommend new rules based on its findings.

The proposed pilot studies and permit program could provide incentives for industry and states to develop safety innovations. Promising technologies, such as electronic braking systems, could improve truck safety but more research and monitoring is needed, the report says.

While trucking firms and shipping groups advocate liberalization of limits, highway-safety advocacy groups, some small trucking firms, and a number of states oppose increases in truck size. And the railroad industry fears the change would divert freight from the rail to highways. Objective data collection and analysis, together with public input, should break the gridlock over size and weight policies.
--Jennifer Burris


Regulation of Weights, Lengths, and Widths of Commercial Motor Vehicles: TRB Special Report 267. Committee for the Study of the Regulation of Weights, Lengths, and Widths of Commercial Motor Vehicles, Transportation Research Board (2002, 270 pp.; ISBN 0-309-07701-X; available from the board, tel. 202-334-3213; $24.00 for single copies).

The committee was chaired by James W. Poirot, chairman emeritus, CH2M Hill Ltd., Mukilteo, Wash. The study was funded by the U.S. Department of Transportation.



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Copyright 2002 by the National Academy of Sciences