Metro serves the District of Columbia, 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 , is located at Metro's deep-level Wheaton station.