The Red Line is a rapid transit line of the Washington Metro system, consisting of 27 stations in Montgomery County, Maryland, and Washington, D.C., in the United States. It is a primary line through downtown Washington and the oldest, busiest, and currently the longest line in the system. It forms a long, narrow "U", capped by its terminal stations at Shady Grove and Glenmont. Rolling stock: WMATA 2000 series WMATA 3000 series WMATA 7000 series WMATA 6000 series