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. On September 22, 1915, there was an explosion during construction of the 23rd Street subway station that caused the tunnel to collapse. Seven people were killed after a blast of dynamite in the subway tunnel destroyed the plank roadway over Seventh Avenue. As a result, a crowded trolley car, and a brewery truck fell into the excavation, accounting for most of the injuries. 23rd 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. This station was renovated in the 1990s.
Station layout
This underground station has two side platforms and four tracks. The two express tracks are used by the 2 and 3 trains during daytime hours. Both platforms have their original mosaic trim line and name tablets of a predominately brown and red color. They also have brown-red i-beam columns at regular intervals with alternating ones having the standard black and white number plate except at either end where they get narrower.
Exits
Each platform has one same-level fare control area in their center and there are no crossunders or crossovers. The northbound platform has the station's full-time turnstile bank and token booth and two staircases going to either eastern corners of 23rd Street and Seventh Avenue. The southbound platform has an unstaffed set of turnstiles and two staircases going up to either western corners of the same intersection.
