The Dual Contracts, which were signed on March 19, 1913, were contracts for the construction and/or rehabilitation and operation of rapid transit lines in the City of New York. The contracts were "dual" in that they were signed between the City and two separate private companies, all working together to make the construction of the Dual Contracts possible. The Dual Contracts promised the construction of several lines in Brooklyn. As part of Contract 4, the IRT agreed to build a branch of the original subway line south down Seventh Avenue, Varick Street, and West Broadway to serve the West Side of Manhattan. The construction of this line, in conjunction with the construction of the Lexington Avenue Line, would change the operations of the IRT system. Instead of having trains go via Broadway, turning onto 42nd Street, before finally turning onto Park Avenue, there would be two trunk lines connected by the 42nd Street Shuttle. The system would be changed from looking like a "Z" system on a map to an "H" system. One trunk would run via the new Lexington Avenue Line down Park Avenue, and the other trunk would run via the new Seventh Avenue Line up Broadway. In order for the line to continue down Varick Street and West Broadway, these streets needed to be widened, and two new streets were built, the Seventh Avenue Extension and the Varick Street Extension. It was predicted that the subway extension would lead to the growth of the Lower West Side, and to neighborhoods such as Chelsea and Greenwich Village. Chambers Street opened as the line was extended south to South Ferry from 34th Street–Penn Station on July 1, 1918, and was served by a shuttle. The new "H" system was implemented on August 1, 1918, joining the two halves of the Broadway–Seventh Avenue Line and sending all West Side trains south from Times Square. An immediate result of the switch was the need to transfer using the 42nd Street Shuttle. The completion of the "H" system doubled the capacity of the IRT system.
Station layout
There are four tracks and two island platforms. The 1 train uses the local tracks, and the 2 and 3 trains use the express tracks. South of this station, the 2 and 3 trains curve east and branch off to Park Place, Fulton Street, Wall Street, and then Brooklyn. The 1 train continues directly south towards its terminal, South Ferry. North of the station are diamond crossovers in both directions, allowing the 2 train to run local during late nights, switching over to the express tracks north of Chambers Street and then heading to Brooklyn; there are no crossovers south of the station due to its close proximity to Park Place. These switches were also used after the September 11, 2001 attacks, when the South Ferry branch of the line was impassable, and the 1 train was routed to Brooklyn in place of the 3 train and all trains that stopped here were local in Manhattan.
Exits
The station's only exits are through the mezzanine above the center of the station. Street stairs lead to four of the five corners of the intersection of Chambers Street, Hudson Streets, and West Broadway. The only corner without a street stair is the wedge between Hudson Street and West Broadway on the intersection's northern side, where the James Bogardus Plaza is located. The southwest corner of the intersection has two stairs. As part of a 2007–2009 renovation, three elevators were installed in the station to make it accessible for people with disabilities under the Americans with Disabilities Act of 1990. The street elevator is on the northwest corner of Chambers and Hudson Streets.
