Using systematic indices to relate traffic load spectra to pavement performance

The application of truck axle load spectra in the Mechanistic Empirical Pavement Design Guide (MEPDG) has brought great advancement in pavement design through quantifying pavement accumulated damage due to individual axle loads. However, how to relate the truck axle load volume and spectra directly to pavement performance remains a practical challenge for pavement engineers. This paper presents a systematic index approach to this issue that characterizes three aspects of traffic loading to pavement performance: volume, load, and damage. Four summary indices were investigated in this study: cumulative truck volume (CTV), cumulative truck load (CTL), equivalent single axle load (ESAL), and relative pavement performance impact (RPPI). The involved concepts and calculation procedures were first introduced, followed by a numerical evaluation analysis of 30 axle load spectra, 18 vehicle class distributions, 2 truck configurations, and 2 pavement types. To demonstrate how these summary indices could be used, a case study was presented. Overall results suggested that the systematic indices introduced in this study had a clear relationship with pavement performance, so it could be used to assist engineers in many ways such as comparing different load spectra, communicating between engineers, and understanding the relationship between traffic and pavement performance for a specific design at any point in time.