Truck Weight Limits

TRB Special Report 225 - Truck Weight Limits: Issues and Options examines various proposals for changes in truck weight regulations. Truck weight limits have always been controversial. They involve trade-offs between the cost to build and maintain highways and the cost to transport goods by truck, and they have implications for highway safety, traffic flow, and highway finance.

Improvements in highway design and vehicle performance have allowed truck weight limits to be revised periodically and generally adjusted upward, and proposals for further revisions appear inevitable. Because of the competitiveness of freight transportation and the ever-increasing demands of shippers, carriers have strong incentives to enhance productivity. Increasing weight is one means to this end. Moreover, there are many specialized trucking configurations that would be within maximum gross weight and axle weight limits, but would not be permitted under the federal bridge formula, which is designed to prevent overstressing of bridges on the Interstates. Heavy, short-wheel-base vehicles, such as dump trucks, can be limited in this way.

The committee that conducted this study concluded that, within limits, the savings in goods movement that would result from allowing heavier trucks would exceed the increased costs for pavements and bridges. A major impediment to making incremental changes in the weight limits, however, is the difficulty highway agencies experience in recouping fees from trucking firms to compensate for the damages they cause. The inability to charge users directly makes most states reluctant to support higher weight limits, even though society as a whole might benefit from the resulting productivity gains. Heavier trucks can also constrict traffic flow and increase risk, but their net effect depends on the extent to which allowing heavier weights might reduce total truck traffic.

The committee found that incremental changes to policies limiting vehicle weights, with attendant net benefits to society, could be achieved with relatively minor adjustments to the federal bridge formula (to allow heavier dump trucks to operate) and with a special permit program. The latter would allow states to permit the operation of heavier trucks provided the carrier followed new safety criteria and the fees collected compensated for the potential infrastructure damage. Moreover, a portion of the fees could be used to enhance enforcement against illegal overloads, which are a serious problem. At the same time, a complicating feature of policies designed to rationalize trucking regulations is that certain types of trucking operations compete head-to-head with railroads, and unless the fees charged are appropriate, such operators can have an unfair advantage that would compromise the viability of rail.