The Mechanistic-Empirical Pavement Design Guide (MEPDG), Interim Edition: A Manual of Practice requires detailed axle loading information in the form of normalized axle load spectra (NALS), number of axles per truck class and axle group types, and axle spacing inputs as part of traffic loading inputs. These data are obtained from weigh-in-motion (WIM) sites.

The objectives of this project were to evaluate the applicability of the existing MEPDG global traffic loading defaults and to use research-quality WIM data from the Long-Term Pavement Performance (LTPP) Specific Pavement Study (SPS) Traffic Data Collection pooled fund study to revise and improve the global default axle loading values. This report provides an assessment of the original MEPDG axle loading defaults, describes WIM data selection criteria, including data reliability assessment, presents findings from the LTPP SPS traffic pooled fund study traffic data review, describes a methodology to generate new MEPDG traffic loading defaults, and provides a description of the new traffic loading defaults and recommendations for their use.