Many agencies use the AASHTO Guide for Design of Pavement Structures to design their pavement systems. The limitation inherent in this method is the empirical nature of the decision process, which was derived from a road test conducted almost 45 years ago in Ottawa, Illinois. The newly released Mechanistic-Empirical Pavement Design Guide (MEPDG), based on NCHRP Study 1-37A, has adopted a mechanistic-empirical pavement design procedure, in which pavement distresses are calculated through calibrated distress prediction models based on material properties laboratory test results and local climatic conditions. The calibrated distress prediction models are based on the critical pavement responses mechanistically calculated by a structural model and coefficients determined through national calibration efforts using the Long- Term Pavement Performance (LTPP) database. The MEPDG requires many parameters to map the calibrated distress prediction models with traffic, environment, and material properties. The present study was conducted to evaluate the relative sensitivity of MEPDG input parameters to asphalt cement concrete (ACC) properties, traffic, and climatic conditions based on field data from two existing Iowa flexible pavement systems. The sensitivities of five MEPDG performance measures (longitudinal cracking, alligator cracking, thermal cracking, rutting, fatigue cracking, and smoothness) were studied by either varying a single input parameter or by varying two input parameters at a time. The findings of this study, presented in this paper, will provide pavement designers a better understanding of those design parameters that affect certain pavement distresses the most and need careful consideration during the design process.
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