When designing pavements (both mix design and structural design), there are three fundamental external design parameters to consider: the characteristics of the subgrade upon which the pavement is placed, the applied loads and the environment. First, the subgrade upon which the pavement is placed will have a large impact on structural design. Subgrade stiffness and drainage characteristics help determine pavement layer thickness, the number of layers, seasonal load restrictions and any possible improvements to subgrade stiffness and drainage itself. Second, the expected traffic loading is a primary design input (both in mix design and structural design). Traffic loads are used to determine pavement composition, layer type and thickness, all of which affect pavement life. Third, the environment has a large impact on pavement material performance. Environmental factors such as temperature, moisture and ice formation can affect pavement durability, binder rheology, structural support and ultimately pavement life and failure.