The Second Avenue Subway (officially the IND Second Avenue Line; abbreviated to SAS) is a future New York City Subway line that has been under discussion for almost a century. The line will run primarily under Second Avenue on the East Side of Manhattan. A first phase of this new line is expected to open on December 30, 2016, having been under construction since 2007. It will run between 96th Street and Second Avenue and the existing 63rd Street Lines, where it will connect to the BMT Broadway Line and the rest of the subway system. The Q train will provide full-time service on phase one and will serve about 200,000 daily riders on the new extension, supplemented by some rush-hour N trains that are making short turns at 96th Street. The full line, if and when funded, will be built in three additional phases, allowing portions to open before the entire line is completed. Upon completion, it would be served by a proposed T train and is projected to serve about 560,000 daily riders. The fully proposed Second Avenue line would consist of 16 stations, 8.5 miles (13.7 km) of tunnel, and cost more than $17 billion.
The line was originally proposed in 1919 as part of a massive expansion of what would become the Independent Subway System (IND). Work on the line never commenced, as the Great Depression crushed the economy. Numerous plans for the Second Avenue Subway appeared throughout the 20th century, but these were usually deferred due to lack of funds. In anticipation of the never-built new subway line, the Second and Third Avenue elevated lines were demolished in 1942 and 1955, respectively. This left the Lexington Avenue Subway as the only rapid transit line on much of Manhattan's east side; today, it is by far the busiest subway line in the United States, with an estimated 1.3 million daily riders.
Construction on the Second Avenue line started in 1972, but was halted in 1975 because of the city's major fiscal crisis; only a few small segments of the line were completed at the time. Simultaneously, construction work on the 63rd Street Lines, which would connect the Second Avenue Line and the IND Queens Boulevard Line to the BMT Broadway Line and the IND Sixth Avenue Line, started in 1969. Work on the 63rd Street line continued even after construction on the Second Avenue line ended. The first segment of the 63rd Street Lines—which opened in October 1989 and extended to 21st Street–Queensbridge in Long Island City, Queens—left provisions for future construction to the Second Avenue Line.
Construction restarted in 2007 following the development of a financially secure construction plan. The Metropolitan Transportation Authority (MTA) awarded a tunneling contract for the first phase of the project to the consortium of Schiavone/Shea/Skanska (S3) on March 20, 2007. This followed preliminary engineering and a final tunnel design completed by a joint venture between AECOM and Arup. Parsons Brinckerhoff is serving as the Construction Manager of the project. A full funding grant agreement with the Federal Transit Administration for the first phase of the project was received in November 2007. A ceremonial ground-breaking for the Second Avenue Subway was held on April 12, 2007. The first phase of the line consists of three new stations and two miles (3.2 km) of tunnel, costing $4.45 billion. The contractor prepared the initial construction site at 96th Street on April 23, 2007. The tunnel boring machine launch box was completed in May 2010, and on May 14, MTA's contractors completed the TBM installation and turned it on. On March 28, 2011, S3, having completed the west tunnel to 65th Street, began drilling for the east tunnel, which completed its run to the Lexington Avenue–63rd Street station's bellmouth on September 22, 2011. As of October 1, 2016, the first phase was 97.2% complete.
The plans for the Second Avenue Subway involve digging 8.5 miles (13.7 km) of new tunnel from 125th Street in Harlem south to Hanover Square, which is located in the Financial District of Lower Manhattan. During Phase 1, the initial phase, the line was to begin at the intersection of Second Avenue and 96th Street, running south to join the BMT Broadway Line via the existing, but rarely used, BMT 63rd Street Line. Phase I stations will be located at 96th Street, 86th Street and 72nd Street. The Q service will be routed to 96th Street. The Q service will initially have a rush-hour service frequency of 7.5 to 10 trains per hour, or one train every 8 to 6 minutes in each direction; by contrast, the IRT Lexington Avenue Line's express tracks (4 5 trains) have an estimated rush-hour frequency of 30 trains per hour, or one train approximately every 2 minutes in each direction. N trains that currently short-turn at 57th Street will be extended to 96th Street using the Second Avenue Subway.
In Phase 2, Q service would be extended to 125th Street and Lexington Avenue. In order to allow for the construction of Phase 3, bellmouths have been constructed at the turnoff to the BMT 63rd Street Line. With the construction of Phase 3 completed, a new T service will operate from 125th Street to Houston Street. After Phase 4 opens, T service will run the full length of the line, from 125th Street to Hanover Square.
The Second Avenue Subway's infrastructure also includes a connection to the BMT Broadway Line, utilizing an existing connection via the 63rd Street Line as part of phase 1. The Q service will operate northward from 57th Street–Seventh Avenue, curving east under Central Park on the 63rd Street Line. The Q train would stop at Lexington Avenue–63rd Street with a cross-platform interchange to the F train before merging with the Second Avenue Line at 64th Street. Thus, after Phase 4 is completed, the residents of Spanish Harlem and the Upper East Side will have direct mass transit service down both Second Avenue and Broadway (via transfer) to the Financial District, and across the Manhattan Bridge to Brooklyn via the Q train.
An additional two-track connection is planned between the line toward Lower Manhattan (around 63rd Street) and the IND 63rd Street Line toward Queens using existing bellmouths that are at 63rd Street and First Avenue. Current plans do not call for it to be used by regular service, but instead to be used for non-revenue moves, and to provide a connection to the Jamaica subway yard The connection would allow for trains to run from the Financial District to Queens if the capacity of the IND Queens Boulevard Line was increased, or if the Queens Bypass was built. Provisions are also being made for an extension north under Second Avenue past 125th Street to the Bronx, and an extension south to Brooklyn