Effect of Traffic Load Characterization (ESAL versus Axle load Spectra) on Rigid Pavement Performance

Traffic is a significant factor in the pavement design process. Traffic characterization includes both the load magnitude and the number of load repetitions for each axle configuration. The two procedures for characterizing traffic in pavement design include: (a) fixed vehicle/axle, and (b) variable traffic and vehicle/axle. The concept of equivalent single axle load (ESAL) was developed in the AASHTO design guide while mechanistic-empirical design method, including the new M-E PDG, uses axle load spectra (ALS) to characterize traffic loadings and repetitions. The main objective of the paper is to assess the effects of different load characterizations (ESAL versus ALS) on rigid pavement performance. This is accomplished by characterizing axle load spectra as a bimodal mixture distribution and then using its parameters to estimate ESALs. Two specific aspects of this study are to: (a) evaluate the effect of equivalent ALS—different axle load spectra which are equivalent in ESALs on predicted rigid pavement performance; and (b) assess the effect of different axle load spectra on pavement performance by varying the number of repetitions to achieve the same ESALs. The results show that assuming axle load spectra which are not site-specific and achieving the desired level of ESALs by changing the number of repetitions may not give reliable estimates of expected pavement performance as compared to site-specific axle load spectra.