Under the Interborough Rapid Transit On October 27, 1904, local and express service opened on the original subway in Manhattan, following the route of the present IRT Lexington Avenue Line from
City Hall to
Grand Central–42nd Street. From there, the service traveled west on
42nd Street on the route of the present
42nd Street Shuttle, and then north on the present
IRT Broadway–Seventh Avenue Line to
145th Street. The current "H" configuration, with separate services along Lexington Avenue and Broadway/Seventh Avenue, was introduced in 1917. Full Lexington Avenue local service from
City Hall to
125th Street opened on July 17, 1918. Local service was extended to
Third Avenue–138th Street on August 1, 1918. On January 7, 1919, trains were extended from 138th Street to Hunts Point Avenue, and to
East 177th Street on May 30, 1920. Service between Hunts Point Avenue and East 177th Street was originally served by a shuttle service operating with elevated cars. On October 24, 1920, service was extended again to
Westchester Square. On December 20, 1920, service was extended to Pelham Bay Park. Service to Pelham Bay Park was served by a mix of through and shuttle trains during the 1920s. On December 21, 1925, the number of Manhattan-bound through trains in the morning rush hour, between 7 a.m. and 8 a.m., was increased from thirteen to eighteen; a 38 percent increase in service. The remainder of trains continued operating as a shuttle service to Hunts Point Avenue. On January 28, 1931, two southbound morning rush hour trips began starting at Pelham Bay Park instead of Hunts Point Avenue. On April 13, 1931, service to Pelham Bay Park was increased. Two additional southbound trips were added, starting at Pelham Bay Park at 5:50 and 6:10 a.m., reducing headways from ten to five minutes. Four northbound trips that terminated at Hunts Point Avenue between 3:53 and 5:05 p.m. were extended to Pelham Bay Park, reducing headways from nine to six minutes, and four northbound trips terminating at Third Avenue-138th Street between 3:36 and 4:48 p.m. were extended to Hunts Point Avenue, reducing headways from to 3 minutes. By 1934, service south of the City Hall station had been discontinued and late-night service ran from Pelham Bay Park to 125th Street only, being replaced by local service on the 4, which had previously run express.
Under the New York City Board of Transportation Effective December 31, 1945,
City Hall station closed with the former Brooklyn Bridge station (renamed to
Brooklyn Bridge–City Hall) being the permanent southern
terminal. However, the 6 train still uses the loop to get from the southbound to the northbound local track at Brooklyn Bridge–City Hall. On May 10, 1946, late-night service was extended from 125th Street to its previous terminus at Brooklyn Bridge when late-night express service on the 4 was restored. Beginning October 14, 1946, weekday rush and Saturday morning rush peak direction express service started, with Pelham Bay trains using the middle track between East 177th Street and Third Avenue–138th Street. This express service saved eight minutes between Third Avenue and East 177th Street. During this time, 6 trains that ran local in the Bronx when express trains operated began to terminate at
East 177 Street to make room for express trains to Pelham Bay Park. On March 7, 1949, the hours of the evening Bronx-bound express service were advanced from 4:30 to 3:30 p.m., and on June 17, 1949, the hours of the morning Manhattan-bound express service were extended from 9:30 to 10:30 a.m. The Lexington–Pelham Bay route became known as the 6. From December 15 to 22, 1950, the weekday rush hour trains from Pelham Bay Park were extended to
South Ferry. On the same day, Bronx express service was expanded to operate during middays, with Pelham Bay trains running express in the peak direction to Brooklyn Bridge in the morning and to Pelham Bay Park in the afternoon. From March to May 1985, one weekday morning rush hour train was extended to
Atlantic Avenue, terminated there, and returned in service to Pelham Bay Park. This service change was made due to track reconstruction taking place at
Penn Station at the time, which forced some
Long Island Rail Road trains to be diverted from Penn Station to
Atlantic Terminal (then known as Flatbush Avenue), disrupting service for LIRR passengers; as a result, morning rush hour service on the routes serving the Lexington Avenue Line was increased in order to transport LIRR passengers who took diverted trains to Flatbush Avenue to reach Manhattan. From January 21 to October 5, 1990, late-night service was extended back to Brooklyn Bridge when late-night express service on the 4 was restored. But the 6 was then cut back to 125th Street for the last time when late-night express service on the 4 in Manhattan was permanently discontinued. Effective October 3, 1999, the 4 and 6 trains once again began to operate local together in Manhattan late nights when the 6 train was permanently extended back to Brooklyn Bridge. After the
September 11, 2001 attacks, 6 service was cut back to Grand Central–42nd Street in the southbound direction. Southbound trains discharged at Grand Central, operated out of service to Brooklyn Bridge, and re-entered service at Brooklyn Bridge in the northbound direction. By the evening of September 12, service was restored to Spring Street, but southbound trains terminated at Bleecker Street, operated out of service to Brooklyn Bridge, and re-entered service at Spring Street. Normal 6 service was restored on September 17. In August 2023, weekend frequencies on the 6 were increased from eight minutes to six minutes. Until the timetable in effect on December 15, 2024, weekdays from 9:00 to 11:00 a.m., select Manhattan-bound trains ran local from Parkchester to
Hunts Point Avenue while select Parkchester-bound 6 trains ran express in that section. After this date, all Manhattan-bound trains ran express and all Parkchester-bound 6 trains ran local in this section. == Route ==