IRT Broadway–Seventh Avenue Line

The IRT Broadway–Seventh Avenue Line (also known as the IRT Seventh Avenue Line or the IRT West Side Line) is a New York City Subway line. It is one of several lines that serves the A Division, 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 IRT Broadway–Seventh Avenue Line is the only line to have elevated stations in Manhattan, with two short stretches of elevated track at 125th Street and between Dyckman and 225th Streets.

The line was constructed in two main portions by the Interborough Rapid Transit Company (IRT), a private operator. The first portion, north of 42nd Street, was opened between 1904 and 1908, and is part of the first subway line in the city. The line ran from City Hall, up the Lexington Avenue Line, across 42nd Street, and up Seventh Avenue and Broadway, before splitting into the Broadway Branch and the Lenox Avenue Line. The second portion of the line, that south of 42nd Street, was constructed as part of the Dual Contracts, which were signed between the IRT, the New York Municipal Railway (a subsidiary of the Brooklyn Rapid Transit Company), and the City of New York. Among the various subway lines that were to be constructed as part of the contracts, the West Side Line was to be extended south along Seventh Avenue to serve Manhattan's West Side.

This extension extended service to the end of Lower Manhattan and into Brooklyn, relieving crowding on the East Side Line, while opening up service to new areas.