The Chrystie Street connection, a section of tunnel completed in 1967, was a major step in the evolution of the New York City subway. It connected the tracks over the Manhattan Bridge to the Sixth Avenue express line, uniting a large portion of the trackage of the former BMT and Independent systems, and instituting one of the most familiar service patterns today.

Prior to 1940, public transportation in New York City was operated by three different competing entities. They were two private corporations, the Brooklyn Manhattan Transit (BMT) and the Interboro Rapid Transit (IRT), which both operated subway and elevated lines throughout the boroughs, and the city run Independent subway system (IND). At that point, the BMT operated various subway and elevated lines in Brooklyn, and a subway under Broadway in Manhattan. BMT service from various lines in southern Brooklyn to Manhattan was available via an East River tunnel to the financial district and the Broadway subway, or over the tracks on the north side of the Manhattan Bridge through Chinatown and under Canal Street to the Broadway subway. At that time the IND Sixth Avenue line, which was fed exclusively from Brooklyn by the Rutguers Street tunnel line (the route of today's F Train) did not contain express tracks.

The IND was built to BMT specifications with an eye toward an eventual unification of the systems, and when this was achieved with the city buy-out of both the BMT and IRT in 1940, plans were made to link the Manhattan Bridge tracks with planned express tracks on the Sixth Avenue line, which would allow rapid easy access from southern Brooklyn to Midtown. This was the Chrystie Street connection, so named because it followed under Chrystie street on its way north from where the tracks submerged right after the Manhattan Bridge until it turned west on Houston to join the Sixth Avenue line before the Broadway-Lafayette station. For the new connection, the former connection to the Broadway subway via Canal Street was shifted to the tracks on the south side of the bridge, and the north side tracks were used for the new connection. The connection, completed and opened in 1967, contained only one station, Grand Street. Grand Street was designed with 'false' walls that could easily be removed to provide cross-platform transfers to a stop on the Second Avenue subway, whose half built tunnels are actually right behind the Grand Street platform walls.

After the connection opened, service via the bridge to the Broadway subway (now on the south side tracks) was discontinued, although the tunnels remained serviceable. All service from the bridge was directed to the Sixth Avenue Line. This connection interconnected the former BMT and IND routes to a sufficient extent that the MTA adopted a universal route system and ceased to use the separate divisions on maps or route descriptions, essentially creating New York city subway routes as we know them today.

As of Spring 2001, the B, D, and Q Trains used the Chrystie street connection in their route from the Manhattan bridge to the Sixth Avenue line.

UPDATE: Construction on the North side Manhattan bridge trackways has closed the Christie Street connection as of July 2001 for a projected four years. Service from Brooklyn once again to follows the Canal street connection to the Broadway subway, and a short shuttle is run to connect the Grand Street station with the Broadway-Lafayette station.