New York City Subway largest rapid transit system in the world by number of stations, with stations in operation ( if stations connected by transfers are counted as single stations). Stations are located throughout the boroughs of Manhattan, Brooklyn, Queens, and the Bronx. The Staten Island Railway is not officially considered part of the subway, as it lacks a rail link with the subway system, so passengers traveling between Staten Island and another borough must take the Staten Island Ferry or an MTA bus; free transfers are allowed to the subway and bus systems. The PATH in Manhattan and New Jersey and the AirTrain
Staten Island Tunnel funded by the city, the tunnel was expected to help expand the then-sparsely populated borough in a similar manner to the population and development explosions seen in Brooklyn and the Bronx. Under the Dual Contracts, three routes were proposed—two to Brooklyn and one to Manhattan—which would connect the Staten Island Railway's rapid transit service (SIRT) to existing subway lines. The Manhattan proposal, often called the "direct route," would have connected with the Interborough Rapid Transit Company (IRT)'s lines under Battery Park, near the current Brooklyn–Battery Tunnel. "Direct Route A" would have utilized a five-section tunnel under the New York Harbor,