In 1967, the Washington Metropolitan Area Transit Authority was created under a 1966 interstate compact encompassing the District of Columbia and portions of the State of Maryland and Commonwealth of Virginia, for the purpose of planning, financing, constructing, and operating a comprehensive mass transit system for the Washington Metropolitan Region. According to Article VI of the Compact the Board shall develop and adopt, and may from time to time review and revise, a mass transit plan for the immediate and long-range needs of the compact region.
The Compact guided the development of the original Adopted Regional System (ARS) in 1968, designed to serve the region as forecast for 1990. Zachary M. Schrag, author of The Great Society Subway, hosts a website including maps and photos of the ARS, as well as an historical account of the building of Metrorail. As planning and engineering continued over the next 20-plus years, the ARS was reviewed and revised, consistent with the Compact. By the mid-1990s, planning had been completed for the ARS. Metro began to look at transit needs beyond those for which the original system had been planned, and to look at a much larger region, as forecast for 2025. Metro’s latest long-range system plan — the Transit Service Expansion Plan– was adopted in 1999.