Washington Metropolitan Area Transit Authority (WMATA) operates Washington Metro, the city's rapid transit rail system, which serves Washington, D.C. and its Maryland and Northern Virginia suburbs. Metro opened on March 27, 1976, and consists of six lines, 98stations, and of track. Metro is the second-busiest rapid transit system in the country and fifth-busiest in North America. It operates mostly as a deep-level subway in more densely populated areas, while most of the suburban tracks are at surface level or elevated. Metro is known for its iconic brutalist-style vaulted ceilings in the interior stations. The longest single-tier escalator in the Western Hemisphere, spanning , is located at Metro's Wheaton station in Maryland.