During the afternoon rush hour of June 22, 2009, a subway train wreck occurred between two southbound Red Line Washington Metro trains in Northeast, Washington, D.C., United States. A moving train collided with a train stopped ahead of it; the train operator along with eight passengers died, and 80 people were injured, making it the deadliest crash in the history of the Washington Metro.

The National Transportation Safety Board (NTSB) investigation found that after a June 17 replacement of a track circuit component at what became the crash site, the track circuit had been suffering from parasitic oscillations which left it unable to reliably report when that stretch of track was occupied by a train. The struck train came to a stop because of traffic ahead. Because the entire train was within the faulty circuit, it became invisible to the Automatic Train Control (ATC) system. The train behind it was therefore commanded to proceed at 55 mph (89 km/h). The operator of the striking train applied the emergency brake after the stopped train came into full view, but there was not enough time to prevent the collision, which occurred at approximately 49 mph (79 km/h).



The Washington Metro (or simply Metro), formally the Metrorail, is a rapid transit system serving the Washington metropolitan area of the United States. It is administered by the Washington Metropolitan Area Transit Authority (WMATA), which also operates the Metrobus and Metrorail services under the Metro name. Opened in 1976, the network now includes six lines, 91 stations, and 117 miles (188 km) of route.Metro serves Washington, D.C., as well as several jurisdictions in the states of Maryland and Virginia. In Maryland, Metro provides service to Montgomery and Prince George's counties; in Virginia, to Arlington and Fairfax counties and to the independent city of Alexandria. Combined with its ridership in the independent Virginia cities of Falls Church and Fairfax, the Metro service area is largely coextensive with the inner ring of the Washington metropolitan area. The system is currently being expanded to reach Dulles International Airport and Loudoun County, Virginia. It operates mostly as a deep-level subway in more densely populated parts of the D.C. metropolitan area (including most of the District itself), while most of the suburban tracks are at surface level or elevated. The longest single-tier escalator in the Western Hemisphere, spanning 230 feet (70 m), is located at Metro's deep-level Wheaton station.Metro is the second-busiest rapid transit system in the United States, in number of passenger trips, after the New York City Subway, and the fifth-busiest in North America. There were 295 million trips on Metro in fiscal year 2018. In June 2008, Metro set a monthly ridership record with 19,729,641 trips, or 798,456 per weekday. Fares vary based on the distance traveled, the time of day, and the type of card used by the passenger. Riders enter and exit the system using a proximity card called SmarTrip.