Establishment of Statewide Axle Load Spectra Data for Texas Mechanistic-Empirical Flexible Pavement Design Using Cluster Analysis

An effort is underway to develop the Texas mechanistic-empirical (TxM-E) flexible pavement design program. Similar to the M-E PDG developed under NCHRP Project 1-37A, the TxM-E intends to employ load-spectra traffic inputs for estimating the magnitude, configuration, and frequency of the traffic loads that are applied throughout the pavement design life. The Texas Department of Transportation (TxDOT) manages 30 weigh-in-motion (WIM) stations and provided classification and weight data used for this study. Evaluating the classification data first, vehicle classification along with the percentage of trucks, average annual daily truck traffic, and monthly adjustment factor were established. Processing axle load data provided the number of axles per truck and axle load spectra for each of the traditional 13 vehicle classes. To develop statewide axle load spectra data, the researchers conducted cluster analysis using vehicle classification distribution data and an analysis of the Class 9 tandem axle load spectra data. Six clusters for both variables were identified and a methodology was established to use those clusters to generate axle load spectra inputs for a given set of truck traffic classification data. Project specific classification data are being collected at over 100 flexible pavement sections by a traffic counter system as an integral task of this study.