Traffic loading, environmental conditions, subgrade soil, and construction and maintenance quality are among the factors that influence pavement performance. Environmental conditions can have a particularly significant impact on the performance of low-volume road pavements. It is intended that the Strategic Highway Research Program performancegraded asphalts ensure that an asphalt binder is selected based on in-service pavement conditions. This new system will enable designers in Ontario to account for differences in climatic conditions and traffic loading, which vary between the southern and northern areas of the province and have always posed a challenge to pavement designers. A deflection-based method was originally developed in the 1970s based on the AASHO road test and the Brampton road test. The design system incorporates elastic layer analysis to determine pavement response. It uses cumulative equivalent single-axle loads, subgrade type, and layer thickness to determine the most effective design. The design system has been recently updated and recalibrated to separate the environment and traffic effects on performance. In effect, the total pavement performance is the cumulative effect of the damage due to the environment and the damage due to traffic. Hence, the differences between roads in southern and northern Ontario can be quantified. The system calculates roughness either in terms of the international roughness index or the riding comfort index, or in terms of performance as a pavement condition index. The mechanistic-empirical performance model can be recalibrated to apply to conditions outside of Ontario. Examples show the relative deterioration and performance curves for various design situations.