Modifications made to the Mechanistic-Empirical Pavement Design Guide (MEPDG) to accommodate the design of a newly constructed composite pavement system featuring a thin portland cement concrete (PCC) layer placed over another PCC layer (PCC-PCC pavement) are described. In previous versions of the MEPDG, a newly constructed PCC-PCC pavement project was considered a bonded PCC overlay of an existing PCC pavement. As a result of this simplification, the MEPDG was not consistent in its predictions for a newly constructed PCC-PCC pavement and its structurally equivalent single-layer analogue. To remedy this inconsistency, researchers suggested modifications to the Enhanced Integrated Climatic Model (EICM) used by the MEPDG in terms of (a) number of locations through the slab used by EICM to determine the thermal gradient and (b) EICM calculation of the subgrade spring stiffness (or k-value). Before-and-after MEPDG sensitivity analyses are included to justify the modifications developed and implemented into the MEPDG with the assistance of the MEPDG development team. This research was conducted under SHRP 2 R21, Composite Pavement Systems.