Development and Influence of Statewide Axle Load Spectra on Flexible Pavement Performance

Abstract

The Mechanistic–Empirical Pavement Design Guide (MEPDG) developed under NCHRP Project 1-37A requires new inputs for traffic characterization. One important traffic input is axle load distribution factors, or axle load spectra. These spectra represent the percentage of the total axle applications within each load interval for single, tandem, tridem, and quad axles. The Arkansas State Highway and Transportation Department sponsored research to develop statewide axle load spectra and evaluate the significance of the developed inputs in the MEPDG. Of 25 weigh-in-motion sites selected for this study, only 10 stations provided good weight data for development of statewide axle load spectra. On the basis of the available weight data, statewide axle load spectra for single, tandem, and tridem axles were developed. However, the data contained few quad axles; therefore, statewide quad-axle load spectra were not generated. A sensitivity analysis related to the axle load spectra showed a significant difference in predicted pavement performance resulting from the statewide and MEPDG default axle load spectra. Therefore, the state-specific axle load spectra are recommended for implementation of the MEPDG in Arkansas and updated periodically unless no significant changes are observed in the future.