The line runs in two parallel tunnels from 59th to 97th Streets with each tunnel carrying two tracks. Initially, the line enters fully enclosed brick tunnels between 67th and 71st Streets, and later between 80th and 96th Streets. The remainder of this segment is located in a beam tunnel structure, which is mostly open-air except for where cross-streets traverse on steel-beam bridges. The tunnels have a vertical clearance of above the running rails. At 97th Street, the line rises onto a viaduct and continues above the median of Park Avenue until it reaches 132nd Street. There, the line crosses the Park Avenue Bridge, a vertical lift bridge, and traverses the Harlem River. The line continues into the Bronx where it diverges into the Hudson Line and the Harlem Line.