Book excerpt: TRB's National Cooperative Highway Research Program (NCHRP) Synthesis 420: Operational and Institutional Agreements That Facilitate Regional Traffic Signal Operations (RTSOPs) identifies and highlights critical attributes of successful RTSOPs across the United States. Regions can use RTSOPs to help improve traffic flow as it crosses from one jurisdiction to another. A central focus of these programs is the coordination of signal timing on multi-jurisdictional arterials; however, RTSOPs can also facilitate the consideration of other traffic operations measures to improve regional mobility. Many RTSOPs have been established through regional metropolitan planning organizations, and successful RTSOPs also have been established by other organizations, including state and local departments of transportation and government corporations.