Roughness is widely regarded as the most important measure of pavement performance. To better understand how and why roughness occurs in pavements, the Long-Term Pavement Performance (LTPP) program recently completed a study entitled, “The Investigation of Development of Pavement Roughness.” A component of the study investigated the changes in three types—Jointed Plain Concrete Pavement (JPCP), Jointed Reinforced Concrete Pavement (JRCP), and Continuously Reinforced Concrete Pavement (CRCP)—of PCC pavement roughness over time and its relationship to design factors, subgrade conditions, and climatic conditions.