Development and Significance of Statewide Volume Adjustment Factors in Mechanistic–Empirical Pavement Design Guide

A new Mechanistic–Empirical Pavement Design Guide (MEPDG) has been developed under NCHRP Project 1-37A. Pavement design procedures recommended for use in MEPDG represent a significant departure from current procedures. The MEPDG requires new traffic inputs for estimating the magnitude, configuration, and frequency of the loads that are applied throughout the pavement design life. The Arkansas State Highway and Transportation Department (AHTD) sponsored research in which one objective was development of statewide truck traffic volume adjustment factors, including class and monthly and hourly distribution factors, and evaluating significance of the developed inputs in the MEPDG. The AHTD provided classification data collected at 55 weigh-in-motion (WIM) sites from 2003 through 2005. Because of missing and inaccurate classification data at several WIM sites, only 23 sites provided classification data suitable for this study. On the basis of selected data, statewide monthly, hourly, and class distribution factors were developed for Arkansas. Analyses using the MEPDG showed the state-specific class distribution factors to have a significant effect on predicted pavement performance, compared with predictions generated by using default distribution values. However, the effect of using state-specific monthly and hourly distribution factors on predicted pavement performance rather than default values was not significant. Therefore, it is recommended that the state-specific class distribution factors be used with the default monthly and hourly distribution factors in the MEPDG. In addition, periodic review and update of statewide class distribution factors, as necessary, are recommended.