Clark Street Tunnel

IRT Broadway–Seventh Avenue Line
Train services that use the IRT Broadway–Seventh Avenue Line have been colored red since 1979.
Overview
Type	Rapid transit
System	New York City Subway
Termini	Van Cortlandt Park–242nd Street South Ferry (Manhattan branch) Borough Hall (Brooklyn branch)
Stations	44
Daily ridership	1,093,105 (south of 96th Street) 348,027 (north of 96th Street)
Operation
Opened	1904-1919
Owner	City of New York
Operator(s)	New York City Transit Authority
Character	Underground (Brooklyn and most of Manhattan) Elevated (125th Street and North of Inwood)
Technical
Number of tracks	1–4
Track gauge	4 ft 8 1⁄2 in (1,435 mm)
Electrification	625V DC third rail

The IRT Broadway–Seventh Avenue Line (also known as the Seventh Avenue Line or the West Side Line) is a New York City Subway line. It is one of several lines that serves the A Division (IRT), stretching from South Ferry in Lower Manhattan north to Van Cortlandt Park–242nd Street in Riverdale, Bronx. The Brooklyn Branch, known as the Wall and William Streets Branch during construction, from the main line at Chambers Street southeast through the Clark Street Tunnel to Borough Hall in Downtown Brooklyn, is also part of the Broadway–Seventh Avenue Line.

The south end of the Brooklyn Branch is unclear. In a 1981 list of "most deteriorated subway stations", the MTA listed Borough Hall and Clark Street stations as part of the IRT New Lots Line. However, as of 2007, emergency exit signs label Borough Hall as an IRT Broadway–Seventh Avenue Line station, and the two parts of Borough Hall are signed as being along the Broadway–Seventh Avenue and IRT Eastern Parkway Lines. The chaining designations "K" (Clark Street Tunnel) and "M" (Joralemon Street Tunnel) join and become "E" (Eastern Parkway Line) at Borough Hall.