The default traffic datasets for the National Cooperative Highway Research Program (NCHRP) Project 1-37A (the MEPDG) were based on the Long-Term Pavement Performance (LTPP) traffic data available in 1998. According to the 1999 interim report, The Development of the 2002 Guide for the Design of New and Rehabilitated Pavement Structures, the quantity and quality of these data were less than expected. Since that time, the LTPP Traffic Data Collection Pooled Fund Study, Transportation Pooled Fund (TPF)-5(004), has greatly increased the quality and quantity of traffic data available through LTPP.
Many pavement construction projects cannot justify the collection of site-specific weigh-in-motion (WIM) data solely for design purposes. Therefore, use of WIM data from other sites or default traffic values is not uncommon. The Mechanistic-Empirical Pavement Design Guide (MEPDG) is sensitive to traffic inputs and the existing default traffic values are inadequate. This project will rectify this situation with the high-quality traffic data now available from the Long-Term Pavement Performance (LTPP) project.