The majority of the Sixth Avenue Line has four tracks, two local and two express. At each end, these pairs of tracks split, giving the line two north and two south ends. One of the north ends is at 57th Street, where two tracks lead south under Sixth Avenue from the IND 63rd Street Line (used by the F local train at all times). The other is just south of 59th Street–Columbus Circle, where a two-track line splits from the IND Eighth Avenue Line at a flying junction (with connections to the local and express tracks), immediately turns east under 53rd Street, and crosses the IND Queens Boulevard Line, which parallels it just to the north. At Seventh Avenue, the southbound track is above the northbound track (the same is true on the Queens Boulevard Line, though north is the opposite direction from the Sixth Avenue Line). These tracks are used by the B and D express trains.