Since the opening of the original New York City Subway line in 1904, and throughout the subway's history, various official and planning agencies have proposed numerous extensions to the subway system. The first major expansion of the subway system was the Dual Contracts, a set of agreements between the City of New York and the IRT and the BRT. The system was expanded into the outer reaches of the Bronx, Brooklyn, and Queens, and it provided for the construction of important lines in Manhattan. This one expansion of the system provided for a majority of today's system.
Even with this expansion, there was a pressing need for growth. In 1922, Mayor John Hylan put out his plan for over 100 miles of new subway lines going to all five boroughs. His plan was intended to directly compete with the two private subway operators, the IRT and the BMT. This plan was never furthered. The next big plan, and arguably the most ambitious in the subway system's history, was the "Second System". The 1929 plan by the Independent Subway to construct new subway lines, the Second System would take over existing subway lines and railroad rights-of-way. This plan would have expanded service throughout the city with 100 miles of subway lines. A major component of the plan was the construction of the Second Avenue Subway. The Stock Market Crash of 1929 put a halt to the plan, however, and subway expansion was limited to lines already under construction by the IND.
During the 1930s and 1940s, the plans were revised, with new plans such as a line to Staten Island and a revised line to the Rockaways. In the late 1940s and 1950s, a Queens Bypass line via the Long Island Rail Road's Main Line was first proposed as a branch of the still-planned Second Avenue Subway. In addition, capacity on existing lines became improved through the construction of strategic connections such as the Culver Ramp, the 60th Street Tunnel Connection, and the Chrystie Street Connection, and through the rebuilding of DeKalb Avenue Junction. These improvements were the only things to come out of these plans. Eventually, these plans were modified to what became the Program for Action, which was put forth by the New York City Transit Authority in 1968. This was the last plan for a major expansion of the subway system. The plan included the construction of the Second Avenue Subway, a Queens Bypass line, a line replacing the Third Avenue El in the Bronx, and other extensions in the Bronx, Queens, and Brooklyn. While ambitious, very little of the plan was completed, mostly because of the financial crisis in the 1970s.
Until the 1990s, there was little focus on expansion of the system because the system was in a state of disrepair, and funds were allocated to maintaining the existing system. In the 1990s, however, with the system in better shape, the construction of the Second Avenue Subway was looked into again. Construction of the Second Avenue Subway started in 2007, and the first phase was completed in 2017. Since the 1990s, public officials and organizations such as the Regional Plan Association have pushed for the further expansion of the system. Projects such as the TriboroRx, a circumferential line connecting the outer boroughs, the reuse of the Rockaway Beach Branch, and the further expansion of the Second Avenue Subway have all been proposed, albeit mostly unfunded.
Triborough System
The Triborough System was a proclamation for new subway lines to the Bronx and Brooklyn. The new lines include the IRT Lexington Avenue Line, IRT Pelham Line, and IRT Jerome Avenue Line. The Manhattan Bridge line described below later became the BMT West End Line, BMT Fourth Avenue Line, the BMT Sea Beach Line, and the Nassau Street loops.
The route of the new subway ... comprises a main trunk north and south through Manhattan Borough on Lexington Avenue and Irving Place from the Harlem River to Tenth St. and on Broadway, Vesey and Church Sts. from Tenth St. to the Battery; two branches in Bronx Borough, one northeast via 138th St. Southern Boulevard and Westchester Ave. to Pelham Bay Park. the other northerly via River Ave. and Jerome Ave. to Woodlawn Road, connecting with the Manhattan trunk by a tunnel under the Harlem River; a Manhattan-Brooklyn line extending from the North River via Canal Street across the East River on the Manhattan Bridge to connect with the Fourth Avenue subway in Brooklyn now being built, which thus becomes an integral part of the larger system; two branches southerly from the Fourth Ave. line extending south to Fort Hamilton and southeast to Coney Island; and a loop feeder line in Brooklyn through Lafayette Ave. and Broadway, connecting with the Fourth Ave. line at one end. and at the other crossing the Williamsburg Bridge and entering the Centre Street Loop subway in Manhattan which is thus also incorporated in the system.
In 1911, William Gibbs McAdoo, who operated a competing subway company called the Hudson & Manhattan Railroad, proposed building a line under Broadway between Hudson Terminal and Herald Square. He later proposed that the Broadway line be tied into the IRT's original subway line in Lower Manhattan. The Broadway line, going southbound, would merge with the local tracks of the IRT Lexington Avenue Line in the southbound direction at 10th Street. A spur off the Lexington Avenue Line in Lower Manhattan, in the back of Trinity Church, would split eastward under Wall Street, cross the East River to Brooklyn, then head down the Fourth Avenue Line in Brooklyn, with another spur underneath Lafayette Avenue.
The Triborough System later became part of the Dual Contracts, signed on March 19, 1913 and also known as the Dual Subway System. These were contracts for the construction and/or rehabilitation and operation of rapid transit lines in New York City. The contracts were "dual", in that they were signed between the City and the IRT and Municipal Railway Company, a subsidiary of the BRT (later BMT).nycsubway.org—The Dual Contracts
Some lines proposed under the Contracts were not built, most notably an IRT line to Marine Park, Brooklyn (at what is now Kings Plaza) under either Utica Avenue, using a brand-new line, or Nostrand Avenue and Flatbush Avenue, using the then-new IRT Nostrand Avenue Line. There were also alternate plans for the Nostrand Avenue Line to continue down Nostrand Avenue to Sheepshead Bay.
Mayor Hylan's plan
On August 28, 1922, Mayor John Francis Hylan unveiled his own plans for the subway system, which was relatively small at the time. His plan included building over of new lines and taking over nearly of existing lines. By the end of 1925, all of these routes were to have been completed. The lines were designed to compete with the IRT and BMT.
Hylan's plan contained the following lines:nycsubway.org—History of the Independent Subway
A line running along Manhattan's West Side, stretching from the edge of the city at Yonkers to 14th Street. It would be a two-track line south to Dyckman Street, a three-track line to 162nd Street, and then-on it would be a four-track line. The line would have two southern branches that would diverge at 14th Street. A connection to the BMT Canarsie Line would use a pair of the tracks, while the other pair would go to Atlantic Avenue and Hicks Street in Brooklyn through an East River tunnel. Then it would turn down to Red Hook. There would also be a loop at Battery Park. Another branch would be built; it would consist of two tracks, and would go between 162nd Street and 190th Street via Amsterdam Avenue. A First Avenue line, consisting of four tracks, would stretch from the Harlem River to City Hall. At 10th Street, the line would cease to be a four-track line, with the line splitting into two branches. One branch would run to a loop near City Hall, while the other would go to a new Lafayette Avenue line in Brooklyn, running via Third Avenue and the Bowery. On the northern end, at 161st Street, the line would split into two 3-track lines. One of the lines would go to Southern Boulevard and Fordham Road; the other would continue to 241st Street after merging with the existing IRT White Plains Road Line at Fordham Road and Webster Avenue. A line from Astoria, Queens, likely connecting to the BMT Astoria Line, across the East River and via 125th Street (near today's Henry Hudson Parkway). A line running from Hunters Point in Queens heading southeast to Lafayette Avenue in Brooklyn. The line would consist of between two and four tracks, and at Lafayette Avenue, the line would split. Two of them would continue as a Lafayette Avenue, but would then become four tracks. The remaining two tracks would run to Franklin and Flatbush Avenues. A new 4-track trunk line along Lafayette Avenue in Brooklyn from Borough Hall to Bedford Avenue. The line would narrow to three tracks to Broadway. Then the line would have continued underneath the BMT Jamaica Line to 168th Street. By running underneath the Jamaica Line, the line would directly compete with the BMT. A two-track connection would also be provided to a First Avenue line. A new line running under Utica Avenue to Flatlands Avenue. The line would be a branch of the IRT Eastern Parkway Line. A four-track Flatbush Avenue line to Emmons Avenue in Sheepshead Bay, before turning west to Surf Avenue in Coney Island via Emmons Avenue. Service to Floyd Bennett Field would be provided with a branch via Flatbush Avenue. The BMT Canarsie Line would be extended past 121st Street in Queens to the BMT Jamaica Line. A new line, which would run from 90th Street to Prospect Avenue, that would go via Fort Hamilton Parkway and 10th Avenue would be used by BMT Culver Line trains. Extension of the BMT Fourth Avenue Line in Brooklyn, south to Bay Ridge–95th Street. Extension of the BMT Fourth Avenue Line east to the Fort Hamilton Parkway Line and the BMT West End Line. A two-track line from the BMT Fourth Avenue Line at 67th Street to Staten Island via the Staten Island Tunnel. Extension of the IRT New Lots Line from New Lots Avenue to Lefferts Boulevard. The IRT Flushing Line would be extended eastward to Bell Boulevard in Bayside via Main Street, Kissena Boulevard, and Northern Boulevard. At Roosevelt Avenue a branch would be constructed off the IRT Flushing Line to Jamaica.
Only some of Hylan's planned lines were built to completion. Completed lines included:
An extension of the Fourth Avenue Line to 95th Street. Two major trunk lines in midtown Manhattan, with one running under Eighth Avenue and one under Sixth Avenue, which already had an elevated line. A crosstown subway under 53rd Street (connecting with the Eighth and Sixth Avenue subways) running under the East River to Queens Plaza (Long Island City), meeting with a Brooklyn–Queens crosstown line, and continuing under Queens Boulevard and Hillside Avenue to 179th Street, where bus service would converge. A subway under the Grand Concourse in the Bronx, diverging from the Eighth Avenue Line in Manhattan at 145th Street and Saint Nicholas Avenue.
Major Phillip Mathews disagreed with the Board of Transportation's plan, and in response, he published a report, on December 24, 1926, titled "Proposed Subway Plan for Subway Relief and Expansion". He said that that congestion would not be addressed for Brooklyn and the Bronx; only the planned Grand Concourse line would alleviate congestion, in this case congestion on the IRT Jerome Avenue Line. There would be little relief on the two lines jointly-operated between the IRT and the BMT. He came up with his own plan. He proposed that the Eighth Avenue Line, through a connection from Fulton or Wall Streets to Chambers Street, be connected to the BMT's lines to Coney Island, with a possible connection at the Manhattan Bridge's south side.