The Red Line of the Washington Metro rail rapid transit system serves 27 stations in Montgomery County , Maryland and the District of Columbia in the United States . It is a primary line through downtown Washington and the oldest and busiest line in the system. It forms a long, narrow "U", capped by its terminal stations at Shady Grove and Glenmont .
The line provides service at 6-minute intervals during the day and 12-minute intervals in the evening.
The Red Line is the only line in the system that does not share its tracks with another Metrorail line. The Amtrak and MARC tracks do, however, run parallel to the Red Line tracks between Washington Union Station and Silver Spring as well as between Twinbrook and Shady Grove stations. These tracks used to be part of the former Batimore & Ohio Railroad route. MARC uses this parallel route when traveling between Washington and Martinsburg, West Virginia. Amtrak, on the other hand, uses this parallel route when traveling the Capitol Limited route between Washington and Chicago Union Station. Although MARC does stop at the Silver Spring and Rockville stations between Washington and West Virginia, Amtrak only stops at Rockville between Washington and Chicago.
Planning for Metro began with the Mass Transportation Survey in 1955 which attempted to forecast both freeway and mass transit systems sufficient to meet the needs of 1980. In 1959, the study's final report included two rapid transit lines which anticipated subways in downtown Washington. Because the plan called for extensive freeway construction within the District of Columbia, alarmed residents lobbied for federal legislation creating a moratorium on freeway construction through July 1, 1962. The National Capital Transportation Agency's 1962 Transportation in the National Capital Region report anticipated much of the present Red Line route, with the Red Line following the Baltimore & Ohio Railroad right-of-way between Silver Spring and Rockville instead of a direct route between Bethesda and Rockville. The route continued in rapid transit plans until the formation of WMATA.
With the formation of WMATA in October 1966,  planning of the system shifted from federal hands to a regional body with representatives of the District, Maryland and Virginia. Congressional route approval was no longer a key consideration. Instead, routes had to serve each local suburban jurisdiction to assure that they would approve bond referenda to finance the system. Because the least expensive way to build into the suburbs was to rely upon existing railroad right-of-ways, the Red Line took much of its present form, except that it continued to feature a further link between its two stems along the Baltimore & Ohio Railroad right-of-way.
By 1969, WMATA had decided on the current routing and stations, except for the extension beyond Rockville to Shady Grove. Montgomery County officials opposed ending the Red Line in downtown Rockville, saying it would cause congestion in the area and use scarce vacant land for a storage yard.  Metro decided to propose to extend the red line one more station to Shady Grove and the U.S. Department of Transportation conditionally approved funding for the extension on July 26, 1975.  Construction on the Red Line began with a groundbreaking ceremony on December 9, 1969.  Construction proved difficult because the National Park Service prohibited a bridge across Rock Creek and required that the Red Line tunnel under that valley, the tunnel in turn caused both the Dupont Circle and Woodley Park stations to be built further underground. The Red Line was proposed to tunnel under Yuma Street from Connecticut Avenue to Wisconsin Avenue, but local residents sued and that court case delayed construction of the tunnel for two years, then WMATA finally won the right to build the tunnel there.
Service on the Red Line (and the Metro as a whole) began on March 27, 1976, with operations between Farragut North and Rhode Island Avenue .  Gallery Place 's opening was delayed due to a court order regarding lack of handicapped access, but it opened in the middle of the line on December 15, 1976. The western end of the line was extended one station to Dupont Circle on January 17, 1977, three stations to Van Ness – UDC on December 5, 1981, five stations to Grosvenor–Strathmore on August 25, 1984 and four stations to Shady Grove on December 15, 1984. The eastern end was extended four stations to Silver Spring on February 6, 1978 – which added Maryland to the system for the first time – two stations to Wheaton on September 22, 1990 and one station to Glenmont on July 25, 1998, completing the line. 
The only time the Red Line shared tracks with another line was from January 27, 1997 to September 17, 1999, when the Green Line Commuter Shortcut used Red Line tracks from Brookland–CUA to Farragut North . A short time after the Green Line branch north of Fort Totten opened in the early 1990s, the Green Line Commuter Shortcut began as a six-month experiment. Passengers could board the Green Line between Greenbelt and West Hyattsville and travel as far as Farragut North without having to transfer; the trains bypassed Fort Totten via a single-track spur between the West Hyattsville and Brookland–CUA stations. Due to its success, the shortcut continued until the mid-city portion of the Green Line was completed in 1999. 
The NoMa – Gallaudet University Metro station (formerly New York Ave–Florida Ave–Gallaudet University), located between Union Station and Rhode Island Avenue – Brentwood , opened on November 20, 2004. It was the system's first in-fill station (i.e., a new station built between existing stations). 
On April 20, 2006, the Washington Metropolitan Area Transit Authority (WMATA), Montgomery County and the state of Maryland announced an agreement to end the off-peak terminations at Grosvenor, having those trains operate instead between Grosvenor and Silver Spring.
The Red Line is undergoing a $212 million improvement program.
2004 Woodley Park accident
On November 3, 2004, an out-of-service Red Line train rolled backward into the Woodley Park – Zoo / Adams Morgan station and hit an in-service train stopped at the platform. No one was killed, but 20 people were injured. A 14-month investigation concluded that the train operator was most likely not alert as the train rolled backward into the station. Safety officials estimated that had the train been full, at least 79 would have died. The train operator was dismissed and Metro officials agreed to add rollback protection to more than 300 rail cars.
2009 train collision
On the evening of June 22, 2009, at 5:03 p.m., two Red Line trains were reported to have collided when traveling between the Takoma and Fort Totten Metro Stations. A stationary train was struck from behind by a second six-car train, resulting in the telescoping of the moving train onto the rear of the stationary train. Nine people were killed in the collision (eight passengers and the train operator) and at least 70 people were injured. It is the deadliest accident in the history of the Washington Metro. The NTSB report on the accident was released on July 27, 2010 and blamed a faulty track circuit, part of the automatic train control system, for causing the crash.  WMATA made a press release detailing changes on July 26 in anticipation of the release. 
Below is a chronological list of dates on which specific portions of the Red Line opened for service. 
|Date ||Event||Total number of stations||Total line length (mi)||Total line length (km)|
|March 29, 1976||Line opens between Farragut North and Rhode Island Avenue – Brentwood||5||4.6||7.4|
|December 15, 1976||Gallery Place opens between existing stations||6||4.6||7.4|
|January 1, 1977||Extension to Dupont Circle opens||7||5.7||9.2|
|February 6, 1978||Extension to Silver Spring opens||11||11.4||18.3|
|December 5, 1981||Extension to Van Ness – UDC opens||14||13.5||21.7|
|August 25, 1984||Extension to Grosvenor–Strathmore opens||19||20.3||32.7|
|December 15, 1984||Extension to Shady Grove opens||23||27.3||43.9|
|September 22, 1990||Extension to Wheaton opens||25||30.5||49.1|
|January 25, 1998||Extension to Glenmont opens||26||31.9||51.3|
|November 20, 2004||NoMa – Gallaudet University Metro station opens between existing stations||27||31.9||51.3|
The Red Line begins above ground at Shady Grove, and parallels CSX Transportation 's Metropolitan Subdivision (served by MARC Brunswick Line trains) to south of Twinbrook. The Red Line then enters a tunnel and curves west to run under Rockville Pike at White Flint. Until Tenleytown, the Red Line follows the route of Rockville Pike and Wisconsin Avenue , in a tunnel except for a bridge over the Washington Beltway (I-495). The tunnel curves east at Tenleytown into Yuma Street to reach the Van Ness-UDC station, curving south there under Connecticut Avenue to south of Farragut Square . A curve under Lafayette Park takes the tunnel east under G Street Northwest through the Metro Center station and the Gallery Place – Chinatown station.
From Gallery Place – Chinatown through Judiciary Square, the line runs southeast, turning east again at D Street to reach Union Station . There it turns north and surfaces adjacent to Union Station's platforms, follows the Washington Terminal yard tracks north to Brentwood where the line turns northwestward and again joins CSX Transportation 's Metropolitan Subdivision tracks, running in a unique gauntlet arrangement with the freight railroad tracks straddling the Metro tracks. The Red Line continues in this manner northwest across the District-Maryland line, through Takoma and past Silver Spring . It reenters a tunnel at 16th Street and heads north under Georgia Avenue to the end at Glenmont . There is a maintenance yard between the NoMa and Rhode Island Avenue stops. 
The Red Line needs 44 trains (10 eight-car trains and 34 six-car trains, consisting of 284 rail cars) to run at peak capacity   Trains leave at 6-minute intervals during the mid-day  and 12-minute intervals during the evenings. 
The line serves the following stations, from northwest to northeast: 
|Service routes||Station||Code||Opened|| Other Metro |
|●||Shady Grove||A15||1984||Northwestern terminal|
|●||●||Bethesda||A09||1984||Purple Line (planned)|
In November 2010, WMATA authorized $37 million in capital improvements on the Red Line. This is a part of $212 million of work on the Red Line scheduled over 2010–2014.  In December 2009, WMATA began construction of a new 1,200-car parking garage to supplement the existing 1,700-car parking garage at the Glenmont station. The new garage opened in April 2012  and was funded by the State of Maryland. 
WMATA is planning a new entrance to the Medical Center station on the east side of Wisconsin Avenue and a pedestrian tunnel to connect the entrance to the station. Currently, about 7,000 riders per day emerge from the station on the west side of Wisconsin, then cross the busy six-lane road to reach Walter Reed National Military Medical Center .  The federally-funded project was scheduled to open in 2015.