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Truck Size/Weight Study Dinged by Outside Agency

Oct 09, 2015 at 08:16 AM CST
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By David Cullen


The Dept. of Transportation’s Comprehensive Truck Size and Weight Limits Study falls short in how it estimates the impact that changes to federal size and weight limits might have on everything from pavement wear to highway safety, according to a peer review of the study released October 8 by the Transportation Research Board of the National Academies of Sciences, Engineering, and Medicine.

The board said the study “lacks a consistent and complete quantitative summary of the alternative configuration scenarios, and major categories of costs -- such as expected bridge structural costs, frequency of crashes, and infrastructure costs on certain roads-- are not estimated.”

DOT had requested TRB to convene a committee to review the congressionally mandated size/weight study, which has yet to be completed. Last year, that committee issued a “letter report” that reviewed preliminary products of the study.

The board’s new “final letter report” goes further. It assesses the methods and data DOT used to come up with estimates of how changing federal truck size and weight limits would impact bridges, pavement, the shares of total freight traffic carried by trucks and other freight modes, safety, and the enforcement of truck regulations.

TRB chided the DOT study for not providing “a framework for understanding all the costs and benefits” based on results of present and past studies, including:

  • A comprehensive list of the categories of costs and benefits
  • The features of a proposed regulatory change that influence each category
  • Approximate sizes of impacts on shippers, truck operators, road users, and the public
  • The categories that are likely to be critical to evaluating regulations

“The committee also identified assumptions and simplifications in the DOT study that might result in misleading estimates of infrastructure, traffic, and safety impacts,” TRB stated.

TRB pointed out that its report “does not take a position on whether or how to change current federal truck size and weight limits," only recommendations for how to better estimate the impact of any changes.

This summer, DOT had declared that “data limitations” uncovered by its research on the impact of increasing truck size and weight limits should at this point preclude changing “relevant laws and regulations.”

In a June 5 letter to Congress detailing the informational deficiency, DOT Under Secretary for Policy Peter Rogoff said that the research effort “revealed very significant data limitations that severely hampered the Federal Highway Administration’s efforts to conclusively study the effects of the size and weight of various truck configurations.”

At that time, DOT said that the next step it would take toward completing its mandated report would involve meeting with an “independent peer review team,” managed by TRB, as well as seeking public comment. DOT stated then that despite the data shortcomings uncovered, the technical reports on size and weight “provide an opportunity for experts in the field to comment in anticipation of the final report to Congress.”

Copies of TRB’s new Review of U.S. Department of Transportation Truck Size and Weight Study can be accessed online.