Implementation Aspects of Traffic Characterization by Means of Axle Load Spectra in the NCHRP Mechanistic Empirical Design Guide

The characterization of highway traffic by means of axle load spectra is one of the most important improvements in the mechanistic-empirical pavement design procedure developed under NCHRP Project 1-37A: Development of the 2002 Guide for the Design of New and Rehabilitated Pavement Structures. This is a very significant and desirable improvement, however, the need for characterizing all traffic by means of a simple summary statistic, such as ESAL, will remain in order to compare traffic levels across facilities. To date, there has not been any comprehensive study on the statistical characteristics of axle load distribution in terms of their effect on pavement performance. This research paper presents and discusses the effects on flexible pavement performance of various axle configurations and axle load distributions measured at various weigh-in motion (WIM) stations in Texas. The estimated performance, in terms of load spectra factor (LSF), is compared with the ESAL assumption and other aggregated measures of traffic. The paper presents the approach that was adopted, an application, results obtained from the analysis and recommendations. In addition, practical implementation issues are discussed. For the covering bastract of this conference see ITRD number E215163.