Conventionally, the resistance of hot-mixed asphalt (HMA) mixtures to permanent deformation is measured by repeated load triaxial (RLT) or repeated shear at constant height (RSCH) testing. The data from these tests have been treated as independent datasets in the prediction of rutting potential in HMA layers. This paper presents a unified permanent deformation model using response measurements made from both tests. The new model quantifies the accumulated permanent shear strain as a function of number of load cycles and factor of safety (FOS). The factor of safety is defined in the q-p space and is evaluated based on the applied stresses and triaxial compression strength properties (cohesion and angle of internal friction). For the specific mixture used in this study, a good correlation was found between the cumulative permanent shear strain and the FOS level, irrespective of the stress conditions and the type of test used.