The result to evaluate the effect of mix temperature on the relationship between pavement density and t/NMAS found that the more rapid cooling of the HMA is a key reason for low density in thinner sections. hence, for thin HMA layers NCAT emphasized the importance of paving rollers staying very close to the paving machine so that rolling can be accomplished prior to excessive colling. The team further identified the in-place air voids content as the most significant factor impacting permeability of HMA mixtures, followed by coarse aggregate ratio and VMA. As the ratio increases, permeability increases, but it decreases as VMA increases at constant air voids content. The variability of permeability between various mixtures is very high; some mixtures are permeable in the range of 8 to 10 percent air voids while others are not. However, to ensure theat permeability is not a problem NCAT recommends an in-place air voids content between 6 and 7% or lower. This appears to be true for a wide range of mixtures regardless of NMAS and aggregate gradation