The mechanistic-empirical (ME) design procedures utilize axle load spectra to characterize the unique traffic loadings for a site. These loading characteristics are employed to calculate pavement response and for subsequent damage computations. Generally, these axle load distributions exhibit a bimodal shape and a mixture of two continuous distributions can be used to model them. In this paper, closed-form solutions are developed to estimate the parameters of a mixture bimodal distribution from data. A mixture of two normal distributions is shown to reasonably fit observed axle spectra. Since it is anticipated that the AASHTO ESAL concept will continue to be used by pavement engineers until the full adoption of ME design methods, a closed-form relationship between ESALs and axle load spectra is proposed. Such a relationship will be useful in estimating the traffic levels from an axle distribution. In addition, the relationship can directly indicate the relative pavement damage caused by axle distributions, and be used to rank axle load spectra within a region or between regions to identify heavier loading corridors.
Abstract