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The Mississippi Transportation Commission (MTC) is opposing any proposed congressional legislation that would modify vehicle weight limitations for the Interstate Highway System and the possibility of “Twin-33’s” being allowed on the interstates. Supporters of the legislation claim that increased truck length and weight limits will increase efficiency and safety.
In a letter to Mississippi’s Congressional delegation, the MTC shows that the proposed length and weight increases not only violate current bridge formulas but will also decrease safety and increase repair costs.
The 1975 bridge formula used by the Federal Highway Administration (FHWA) protects the structural integrity of bridges from damage caused by heavy trucks. The six-axle configuration proposed in 2015, which has been proposed again this year, will violate this formula.
FHWA tested one 91,000 pound six-axle combination in the Comprehensive Truck Size and Weight Limit Study, but the configuration tested could only carry up to 45,000 pounds on the three-axle and still be in compliance with the bridge formula.
Last year, the U.S. Department of Transportation (USDOT) released its Final Truck Size and Weight Report to Congress, recommending there be no changes in current truck size and weight limits. The USDOT report concluded that there was not enough data to support the claims that bigger trucks would be safer.
According to the American Society of Civil Engineers (ASCE), one in nine bridges is structurally deficient. In Mississippi, that number is one in eight. Overweight trucks cause a disproportionate amount of damage to the state’s deteriorating roads and bridges compared to passenger vehicles. An 18,000-pound truck axle does over 3,000 times more damage to pavement than a typical passenger vehicle axle. Increasing the weight of a heavy truck by only 10 percent, increases damage by 33 percent.
“The limited data available actually shows that heavier trucks have higher crash rates and that longer trucks take 22 feet longer to stop, causing considerable bridge damage,” said the MTC in its letter to Congress. “Our maintenance efforts are already seriously underfunded. This type of legislation would further contribute to the destruction of bridges and to the cost of repairs and rehabilitation on states, and ultimately the public.”
To view the full letter from the MTC to Congress, click here. For more information, visit GoMDOT.com.
