The Green Line is one of the six heavy rail subway lines that make up the Washington Metro rapid transit system in the Washington, D.C., metropolitan area. The Green Line consists of 21 stations, with termini at Branch Avenue and at Greenbelt. The Green Line runs through Prince George's County, Maryland, and the District of Columbia. It was the last line in the original Metrorail plan to be constructed, and is one of three north–south lines through the city of Washington.