How much do different rehabilitation treatments reduce roughness? The answer to this question can be found in a recently completed study entitled, “The Investigation of Development of Pavement Roughness.” Initiated by the Long Term Pavement Performance (LTPP) program, a component of this study investigates selected asphalt concrete (AC) rehabilitation treatment factors in reducing roughness. Specific factors consiered include: overlay mix type (recycled and virgin), overlay thickness, and surface preparation of the existing AC surface prior to overlay (minimal and intensive preparation).