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In an ongoing transportation pooled fund study on refining Superpave binder specifi cations, 12 full-scale pavement lanes with various modified asphalts were constructed at the Federal Highway Administrations (FHWA) Pavement Test Facility (PTF) in Virginia. The hot mix asphalt (HMA) layers were built on an aggregate base course used in a previous exper iment and partially replaced and re-compacted during the reconstruction. The goal during the reconstruction was to achieve a uniform base course across the 12 lanes by controlling the com paction density. Three in situ tests were conducted on the top of the base course during the construction. They were Nuclear Density (ND) gauge, Humboldt Stiffness Geogauge?(HSG), and falling weight deflectometer (FWD). This paper summarizes the results and evaluations from these in situ measurements.The results show the dry density values measured by the Nuclear Density gauge were not statistically different across the 12 lanes, but the FWD showed significant variations in composite modulus across the same lanes. Analyses were conducted on the effect of variations in the base composite modulus on fatigue cracking and rutting in the pavements. The analyses indi cate that the variations in the base composite modulus could result in significant differences in pavement fatigue life but the pavement rutting distress was not very sensitive to the base layer variations over the range encountered.