Effect of Traffic Load Input Level on Mechanistic–Empirical Pavement Design

Abstract

This study investigated the effect of the input level of axle load spectra on performance predictions obtained with the Mechanistic–Empirical Pavement Design Guide (MEPDG). Traffic monitoring data collected from 50 weigh-in-motion (WIM) stations distributed across the state of Ohio were analyzed to obtain site-specific and regional axle load spectra. The site-specific axle load spectra were calculated for each axle group (single, tandem, tridem, and quad) and truck class (Classes 4 through 13). The regional axle load spectra were developed on the basis of statewide averages and cluster analysis. The statewide average was calculated with information from all sites, whereas the cluster averages were created on the basis of Class 9 tandem axles. Baseline designs for new flexible pavements were defined in the MEPDG for each of the WIM sites having available data, and site-specific, statewide average, cluster average, and MEPDG default axle load spectra were used to assess the impact of the input level of axle load spectra on the performance of the pavement structure. The statewide average and the cluster averages were found to yield similar predictions of pavement performance, with the cluster averages being slightly closer to the site-specific predictions of pavement performance. In addition, the MEPDG default axle load spectra were found to underestimate the pavement service life significantly and, if used for design purposes, would result in overly conservative pavement layer thicknesses. Therefore, the authors recommend the use of site-specific axle load spectra when possible in the design of flexible pavements. However, if site-specific data are not available, statewide average axle load spectra should be used.