Development of Regional Traffic Data for the Mechanistic–Empirical Pavement Design Guide

To obtain full benefits from the new Guide for Mechanistic–Empirical Design of New and Rehabilitated Pavement Structures (MEPDG), it is necessary to characterize pavement traffic loads using detailed traffic data, including axle load spectra. Preferably, the detailed traffic data should be site specific. In the absence of site-specific traffic data, default input data need to be used. Truck traffic data, collected as part of a periodic commercial traffic survey, were used to obtain the best possible default values for traffic input parameters required for the MEPDG. Default traffic input parameters were developed for two Ontario, Canada, regions. The sensitivity of the predicted pavement performance to changes in traffic input parameters was explored. There are several notable differences between the default traffic data inputs included in the MEPDG software and the regional traffic data inputs developed for Ontario, particularly in terms of axle load spectra. Axle load spectra for Ontario have a smaller number of heavily overloaded axles, and the peaks between loaded and unloaded axles are more pronounced. There are also notable differences between axle load spectra for northern and southern Ontario. Compared with southern Ontario, northern Ontario axle load spectra are heavier and have a large proportion of fully loaded axles. The number and type of trucks, followed by the axle load spectra, have the predominant influence on the predicted pavement performance. The MEPDG contains several input parameters that do not have any significant influence on the predicted pavement performance, namely, hourly traffic volume adjustment factors and axle spacing.