A bipartisan group of Representatives asked the Department of Transportation to consider the impact of heavier trucks on local roads and bridges as it studies national size and weight limits.

“We are concerned that heavier or longer trucks could divert significant amounts of freight to highways, resulting in an increase in heavy truck traffic and increased costs to states and localities,” said the 45 Representatives in an August 7 letter to DOT Secretary Anthony Foxx.

The Federal Highway Administration is well into a comprehensive size and weight study that is intended to inform congressional debate over whether or not to raise national limits.

Congress called for the study in last year’s highway bill, in preparation for the new bill that is due a year from October.

FHWA is studying three configurations: the current 5-axle, 80,000-pound standard; a 5-axle, 88,000-pound combination; and the 6-axle, 97,000-pound combination.

It also is considering an additional three configurations, possibly including twin 33-foot trailers, Rocky Mountain Doubles, Turnpike Doubles and triples.

The study will look at the safety and economic implications of changing the federal limits.

It will compare trucks operating at current size and weight limits to bigger and heavier trucks on the basis of crash rates and other safety risk factors, as well as the costs of effective enforcement, and the impact of the equipment on pavements and bridges. It also will look into the impact on truck-rail competition.

The Representatives said they particularly need information on the impact of intermodal shifts arising from any change in the limits.

“Accurately assessing the likely significant changes to all modes of transportation will be paramount to making any reliable findings about truck traffic volumes, infrastructure condition, environmental quality, cost responsibility and how the communities we represent will be affected,” they wrote.