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The Washington Metro system was conceived as an alternative to constructing a large freeway system throughout the Washington, D.C., area. It was partially financed with funds originally dedicated to highway construction. Construction began in 1969, and in 1976 the first section of the Metro system opened along the Red Line between the Farragut North and Rhode Island Avenue stations in Washington, D.C. Throughout the 1970s and 1980s, more stations were opened in the city and the suburban communities of Arlington County, the City of Alexandria, and Fairfax County in Virginia as well as Montgomery and Prince George's Counties in Maryland. By 1991, five rail lines were open: the Red, Orange, Yellow, Green, and Blue Lines. The system, as originally planned, was completed in 2001 with the extension of the Green Line to Branch Avenue. In 2004, three stations were opened: an extension of the Blue Line to the Morgan Boulevard and Downtown Largo stations and the first infill station, NoMa–Gallaudet U. The Silver Line opened in two phases, adding five stations in 2014 and six in 2022. On the Yellow and Blue Lines, an additional infill station at Potomac Yard–VT opened on May 19, 2023.
Nine Metrorail stations are officially designated transfer stations, although other intermediate stations also allow passengers to transfer between lines. Four of these stations have separate, perpendicular upper and lower levels, which open at different times. Two other transfer stations, Rosslyn and Pentagon, have parallel stacked platforms. Ten stations are termini (stations at the end of lines); several other non-terminus stations are used to short turn trains in regular service.
As of May 2016, Union Station was the busiest station in the system, with an average of 28,864 passenger boardings per weekday. Nine of the top ten busiest stations are in the District of Columbia. Metro Center, a Blue, Orange, Silver, and Red Line transfer point, is the busiest transfer station, with 24,160 boardings. Shady Grove in suburban Montgomery County, Maryland was the busiest terminus with 11,696 passenger boardings per weekday.
Stations noted in this list twice with upper and lower levels are considered by WMATA as a single station. The levels are noted separately here because they opened on different dates.
Average daily rail entries for Silver Line extension stations are from November 15, 2022, to December 31, 2022.
Schrag, Zachary (2006). The Great Society Subway: A History of the Washington Metro. Johns Hopkins University Press. ISBN0-8018-8246-X.
"WMATA History" (PDF). Washington Metropolitan area Transit Authority. 2007. Archived from the original (PDF) on October 15, 2012. Retrieved August 26, 2015.
^ "Metro Facts" (PDF). Washington Metropolitan area Transit Authority. 2014. Archived from the original (PDF) on February 22, 2016. Retrieved August 26, 2015.
^ "Metro Media Guide" (PDF). Washington Metropolitan Area Transit Authority. 2010. Archived from the original (PDF) on July 28, 2012. Retrieved July 14, 2011.