Development of truck axle spectra from Oregon weigh-in-motion data for use in pavement design and analysis.

Four weigh-in-motion (WIM) sites in Oregon, representing high, moderate, and low average daily truck traffic (ADTT) volumes, were selected to characterize axle weight and spacing spectra on Oregon state highways. Seasonal variations were considered by investigating data occurring over the four seasons: winter, spring, summer, and fall. WIM data were cleaned and filtered, and analyzed. Axle data, including group and individual axle weights as well as axle spacings, were evaluated. Hourly truck volumes were also examined. Results were summarized and statistics were developed for the characteristic data. The characterized Oregon WIM axle data were incorporated into the Mechanistic Empirical Pavement Design Guide (MEPDG) software program to permit State and ADTT volume-specific axle weight spectra, average axle group spacing, and hourly volume data to be used in the pavement analysis/design. In order to implement the Oregon WIM data, a “virtual” truck classification was created in the MEPDG program. The Oregon-specific data that were required for input into the MEPDG were hourly truck volume distribution, site-specific axle weight data, average number of axles per truck, and average axle spacing. Implementation of the Oregon WIM data will improve the pavement design process in the State by designing to more realistic local loading conditions.