The south end of the Brooklyn Branch is unclear. In a 1981 list of "most deteriorated subway stations", the MTA listed Borough Hall and Clark Street stations as part of the IRT New Lots Line. However, as of 2007, emergency exit signs label Borough Hall as an IRT Broadway–Seventh Avenue Line station, and the two parts of Borough Hall are signed as being along the Broadway–Seventh Avenue and IRT Eastern Parkway Lines. The chaining designations "K" (Clark Street Tunnel) and "M" (Joralemon Street Tunnel) join and become "E" (Eastern Parkway Line) at Borough Hall.
The line is also known as the IRT West Side Line, since it runs along the west side of Manhattan; the part north of 42nd Street was built as part of the first subway in New York. The line serves places such as Lincoln Center, Columbia University, and the City College of New York.
Train services that use the IRT Broadway–Seventh Avenue Line are colored tomato red on subway signage and literature. The line is served by the 1 2 3 trains, which operate together over much of the line. In the past, the 1 train operated as a skip-stop service in tandem with the 9, which was discontinued after May 27, 2005; from 1994 onward, this skip-stop separation existed only in Upper Manhattan during rush hours.
An unused third track along much of the line north of 96th Street has been used in the past for peak direction express service, at least between 96th Street and 137th Street. This center track is currently used only during construction reroutes. There is another unused third track between Dyckman Street and Van Cortlandt Park–242nd Street. Meanwhile, throughout this three track, three yards have connections to the line. The 240th Street Yard is located between Van Cortlandt Park-242nd Street and 238th Street. This yard holds 21 layup tracks and holds the entire rolling stock for the 1. The next yard, thold few trains that are used during rush hours and cleans and overhauls the entire line's fleet. Finally, the 137th Street Yard has six tracks, which hold rush hour turn around trains.
The Clark Street tunnel carries the 2 3 trains under the East River between the boroughs of Manhattan and Brooklyn. It was opened for revenue service on Tuesday, April 15, 1919, relieving crowding on the Joralemon Street tunnel and providing passengers with a direct route to travel between Brooklyn and the west side of Manhattan. It is about 5,900 feet long, with about 3,100 feet underwater.
Construction of the tunnel began on October 12, 1914, using a tunneling shield in conjunction with compressed air. The tunnel was designed by civil engineer Clifford Milburn Holland, who would later serve as the first chief engineer of the Holland Tunnel. The north tube was holed through on November 28, 1916.
On December 28, 1990, an electrical fire in the Clark Street tunnel trapped passengers on a subway train for over half an hour, killed two people, and injured 149 passengers.
Operation of the first subway began on October 27, 1904, with the opening of all stations from City Hall to 145th Street on the West Side Branch. Service was extended to 157th Street on November 12, 1904, as the station was delayed because there was still painting and plastering work going on in the station. The West Side Branch was extended northward to a temporary terminus of 221st Street and Broadway on March 12, 1906. This extension was served by shuttle trains operating between 157th Street and 221st Street. However, only the Dyckman Street, 215th Street, and 221st Street stations opened on this date as the other stations were not yet completed. The 168th Street station opened on April 14, 1906. The 181st Street station opened on May 30, 1906, and on this date express trains on the Broadway branch began running through to 221st Street, eliminating the need to transfer at 157th Street to shuttles. The station at 207th Street was completed in 1906, but since it was located in a sparsely occupied area, the station was opened in 1907. The original system as included in Contract 1 was completed on January 14, 1907, when trains started running across the Harlem Ship Canal on the Broadway Bridge to 225th Street, meaning that 221st Street could be closed.
Once the line was extended to 225th Street on January 14, 1907, the structure of the 221st Street was dismantled and was moved to 230th Street for a new temporary terminus. Service was extended to the temporary terminus at 230th Street on January 27, 1907. An extension of Contract 1 north to 242nd Street at Van Cortlandt Park was approved in 1906 and opened on August 1, 1908. (The original plan had been to turn east on 230th Street to just west of Bailey Avenue, at the New York Central Railroad's Kings Bridge station.) When the line was extended to 242nd Street the temporary platforms at 230th Street were dismantled, and were rumored to be brought to 242 Street to serve as the station's side platforms. The 191st Street was not open until January 14, 1911 because the elevators and other work at the station had not yet been completed.
Between 1904 and 1908, one of the main service patterns was the West Side Branch, running from Lower Manhattan to Van Cortlandt Park via what is now the Lexington Avenue, 42nd Street, and Broadway–Seventh Avenue Lines. There was both local and express service with express trains using the express tracks south of 96th Street. Some express trains ran to Atlantic Avenue in Brooklyn via the Joralemon Street Tunnel during rush hours while all other trains turned around at City Hall or South Ferry.
On September 22, 1915, there was an explosion during construction of the 23rd Street subway station that caused the tunnel to collapse.
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 (the Interborough Rapid Transit Company and the Brooklyn Rapid Transit Company), 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, before 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 a "Z" system 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. 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.
South of Chambers Street, there were to be two branches constructed. The first branch would run to the Battery via Greenwich Street, while the second branch would turn eastward under Park Place and Beeckman Street and down William Street running under the East River through a tunnel before running under Clark Street and Fulton Street until it reaches a junction at Borough Hall with the existing Contract 2 IRT Brooklyn Line.
On June 3, 1917, the first portion of the Broadway–Seventh Avenue Line south of Times Square–42nd Street, a shuttle to 34th Street–Penn Station, opened; a separate shuttle service, running between 42nd and 34th Streets, was created. This short extension was opened even though the rest of the route was not yet completed in order to handle the mass of traffic to and from Pennsylvania Station. Only the northern part of the station was opened at this time, and piles of plaster, rails, and debris could be seen on the rest of the platforms. This shuttle was extended south to South Ferry, with a shorter shuttle on the Brooklyn branch between Chambers Street and Wall Street, on July 1, 1918. Finally, 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.
The local tracks ran to South Ferry, while the express tracks used the Brooklyn Branch to Wall Street, extended into Brooklyn to Atlantic Avenue via the Clark Street Tunnel on April 15, 1919. Extensions of the Eastern Parkway Line and the connecting Nostrand Avenue Line and New Lots Line opened in the next few years, with the end result being that West Side trains ran to Flatbush Avenue or New Lots Avenue.
In 1948, platforms on the line from 103rd Street to 238th Street were lengthened to 514 feet to allow full ten-car express trains to platform. Previously the stations could only platform six car local trains. The platform extensions were opened in stages. On April 6, 1948, the stations from 103rd Street to Dyckman Street had their platform extensions opened, with the exception of the 125th Street, which had its opened on June 11, 1948. On July 9, 1948, the platform extensions at stations between 207th Street and 238th Street were opened for use at the cost of $423,000.
Under a $100,000,000 rebuilding program, increased and lengthened service was implemented during peak hours on the 1 train. Switching at a junction north of 96th Street, delayed service as trains from the Lenox Avenue Line which ran local switched from the express to the local, while trains from the Broadway Branch that ran express switched from the local to the express. This bottleneck was removed on February 6, 1959. All Broadway trains were locals, and all Lenox Avenue trains were expresses, eliminating the need to switch tracks. All 3 trains began to run express south of 96th Street on that date running to Brooklyn. 1 trains began to run between 242nd Street and South Ferry all times. Trains began to be branded as Hi-Speed Locals, being as fast as the old express service was with 8-car trains consisting of new R21s and R22s on the line. During rush hour in the peak direction, alternate trains, those running from 242nd Street, made no stops except 168th Street between Dyckman and 137th Streets in the direction of heavy traffic. The bypassed stations were served by locals originating from Dyckman Street.
The improved service could not be implemented until the platform extensions at stations on the line were completed. The original IRT stations north of Times Square could barely fit five or six car locals based on whether the trains had one or two ends with cars that had manually operated doors. In 1958, the platform extensions at the local stations were nearly completed, but there were more problems with the platform extensions at the two express stations, 72nd Street and 96th Street. To make room for the platform extension at 72nd Street, the track layout was changed. However, in order to fit the platform extension at 96th Street, the local tracks and the outside walls had to be moved. A new mezzanine with stairways to the street was built between West 93rd Street and West 94th Street. Since the 86th Street and 96th Street stations had their platforms extended in order to accommodate 10-car trains, the 91st Street station was closed on February 2, 1959 because if could not have its platforms extended since they would already be to close to the other two stations.
During the 1964–1965 fiscal year, the platforms at Park Place, Fulton Street, Wall Street, Clark Street and Borough Hall were lengthened to 525 feet to accommodate a ten-car train of 51-foot IRT cars.
On August 21, 1989, the 1/9 weekday skip-stop service started. The plan was to have skip-stop service begin north of 116th Street–Columbia University, but due to criticism, most notably that riders did not want 125th Street to be a skip-stop station, skip-stop service operated north of 137th Street–City College between the hours of 6:30 am and 7:00 pm. All 1 trains skipped Marble Hill–225th, 207th, 191st and 145th Streets, while all 9 trains skipped 238th, 215th, Dyckman and 157th Streets. On September 4, 1994, midday skip-stop service was discontinued, and 191st Street was no longer a skip-stop station.
After the September 11 attacks, all 1 trains had to be rerouted since the IRT Broadway–Seventh Avenue Line ran directly under the World Trade Center site and was heavily damaged in the collapse of the Twin Towers. It ran only between 242nd Street and 14th Street, making local stops north of and express stops south of 96th Street. The skip-stop service with the 9 train was suspended. On September 19, after a few switching delays at 96th Street, service was changed. All 1 trains made all stops from 242nd Street to New Lots Avenue via the Clark Street Tunnel and IRT Eastern Parkway Line, to replace all 3 trains (which terminated at 14th Street) at all times except late nights, when it terminated at Chambers Street in Manhattan instead. On September 15, 2002, all 1 trains returned to the South Ferry Loop and 9 skip-stop service was reinstated. But Cortlandt Street, which was directly underneath the World Trade Center, was demolished as part of the clean-up and will be rebuilt as part of the World Trade Center Transportation Hub.
On May 27, 2005, the 9 train was discontinued and all 1 trains now made all stops. The skip-stop service made less sense by 2005 because of the increased number of trains being run and the higher ridership at the bypassed stations; the MTA estimated that eliminating skip-stop service only added 2 1⁄2 to 3 minutes of travel time (for passengers at the northernmost stations at 242nd Street and 238th Street) but many passengers would see trains frequencies double, resulting in decreased overall travel time (because of less time waiting for trains).
On March 16, 2009, the new South Ferry station opened, replacing the original loop station. The loop station could only accommodate the first five cars of a train and it required the use of gap fillers. The new station was built as a two-track, full (10-car)-length island platform on a less severe curve, permitting the operation of a typical terminal station. The newer station does not have a connection to the IRT Lexington Avenue Line, and is located underneath the loop station. The MTA claimed that the new station saved four to six minutes of a passenger's trip time and increased the peak capacity of the 1 service to 24 trains per hour, as opposed to 16 to 17 trains per hour with the loop station. This was the first new station to open since 1989 when the IND 63rd Street Line stations opened.
1 service was affected by Hurricane Sandy in October 2012, following serious flood damage at South Ferry. Rector Street served as a temporary terminal until April 4, 2013, when the 1 returned to the reopened loop station, also serving as a temporary terminal until the new South Ferry Station opens again in June 2017. Also due to Hurricane Sandy, service would not run in the Clark Street Tubes on weekends and late nights between June 2017 and June 2018, affecting 2, 3, 4, and 5 service on weekends and late nights. During these times, Park Place, Fulton Street, Wall Street, Clark Street, Borough Hall, and Hoyt Street would be closed.
The following services use part or all of the Broadway–Seventh Avenue Line, whose services' bullets are colored tomato red: