The determination of a single test temperature for asphalt mixtures to simulate major distresses on flexible pavement is quite significant in characterizing asphalt mixtures. It is apparent that the practical use of a single temperature would reduce testing needs as well as relevant analysis efforts. Effective temperature (T sub eff) can be defined as a single test temperature at which an amount of distress would be equivalent to that which occurs from the seasonal temperature fluctuation throughout the annual temperature cycle. The primary goal of this study was to develop the T sub eff for permanent deformation and fatigue cracking of asphalt mixtures. The predicted distress for both permanent deformation and fatigue cracking that is used to optimize the T sub eff models and to find optimal coefficients was obtained by running the latest version of the Mechanistic-Empirical Pavement Design Guide (MEPDG). A feature of the developed T sub eff models is that they incorporate comprehensive climatic characteristics as well as loading frequency. By incorporating those parameters, it was observed that the model is well correlated with the MEPDG distress results. Therefore, the use of the T sub eff models is recommended as a means to suggest a testing temperature in the simple performance test (SPT) for the distresses. This research work addresses the integration of the MEPDG methodology (NCHRP 1-37A and NCHRP 1-40D) with the SPT (NCHRP 9-19) to develop the T sub eff models for the two distresses. Furthermore, the T sub eff methodology will be incorporated into the performance-related specification being developed (NCHRP 9-22).