Pavement-Dependent Load Limits

Abstract

South Dakota statutes limit the weight of nonsteering axles to 500 lb/in. of tire width. The load allowance for single axles or spread tandem axles with wide-base tires is less than the axle load limit for dual tires. The objective of this research is to assess the potential impact of policy change if the load limit on wide-base tires is increased to be the same as the load limit on dual tires. First, a comprehensive literature review was conducted. Results indicated that the impact of wide-base tires on pavement damage varied, depending on pavement structure and damage mechanism. Pavement response and performance data were obtained from previous studies to calculate damage ratios between wide-base tires and dual tires with the same load. Different pavement failure mechanisms (fatigue cracking, top-down cracking, primary rutting, and subgrade rutting) were applied. Cost functions were then developed by relating the life-cycle cost of four typical asphalt pavement structures used in South Dakota to design traffic levels. The impact of the policy change on the cost of pavement damage was estimated by using detailed traffic data for each road segment in the state highway network. It was found that the cost of pavement damage increased because of wide-base tires on thin asphalt pavements commonly used in secondary roads. However, the impact of wide-base tires on Interstate highways was minimal. In addition, the environmental benefits brought about by the use of wide-base tires were equally significant, especially when the reduction in fuel consumption and air pollution was considered.