Comprehensive Truck Size and Weight Limits Study: Pavement Comparative Analysis Technical Report

Chapter 5: Current Impacts of Overweight Vehicles

5.1 Impacts of Overweight Vehicles on Pavement Costs

Vehicle-related pavement costs are incurred based on the axle loads that vehicles impose on a roadway. Current regulations allow single axle weights of 20,000 lbs. and tandem axle weights of 34,000 lbs. on the Interstate system, but many vehicles have axle weights in excess of those limits because of special permits, lack of enforcement, or other factors.

The study analyzed the effect of overweight axles in current operations, defining overweight as single axles weighing more than 20,500 lbs. and tandem axles weighing more than 35,000 lbs. to be consistent with the axle weight group boundaries used in the vehicle weight analysis and in recognition of the fact that any regulation has a small margin of enforcement tolerance associated with it.

The approach used to analyze these impacts was straight-forward. For a selected subset of pavement sections (the medium-volume traffic sections on the Interstate system), Pavement ME Design® software was applied twice—once with the base case of traffic, and once with all axles over the specified limit removed from the traffic mix. Comparing the results of the runs would allow estimation of how many years it would take under each traffic mix for a pavement to reach the end of its initial service interval—the time when some sort of rehabilitation action would be needed,

Initial service intervals were found to increase significantly for both flexible and rigid pavement sections (except in the case of one rigid pavement section that did not reach the end of its initial service interval during the analysis period).

Flexible pavement initial service intervals increased by between and 19 percent and 34 percent and rigid pavement initial service intervals increased by between 0 percent and 10 percent when overweight axles were removed from the traffic mix. The initial service interval changes for each of the medium volume Interstate pavement sections are contained in Appendix O. LCCs would decrease correspondingly.

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