Their route emblems, or "bullets", are colored brown since they use the BMT Nassau Street Line in Lower Manhattan.

Additional 14 trains, between Eastern Parkway or Atlantic Avenue on the Canarsie Line and Manhattan provided rush-hour local service on Broadway.

The Atlantic Avenue trips remained, and rush-hour trains continued to serve Rockaway Parkway (Canarsie), though they did not use the Broadway express tracks.

[citation needed] On the Manhattan end, the first extension was made on September 16, 1908, when the Williamsburg Bridge subway tracks opened.

The next change was made on July 1, 1968, when the Chrystie Street Connection tracks to the Williamsburg Bridge opened.

A new service, KK, was instituted that provided skip-stop service from 168th Street/Jamaica along with the QJ in both AM and PM rush hours; because of the limited skip-stop time spans, other terminals for the KK included Rockaway Parkway, Atlantic Avenue, Eastern Parkway and 111th Street.

[25][26] On January 2, 1973, the QJ, which was the longest route in the transit system, was cut back to Broad Street and redesignated the J; and the M was extended to Coney Island in its place.

[29] The K was discontinued entirely on August 30, 1976,[30] eliminating the J skip-stop and express service east of Myrtle Avenue in the evening rush hour.

One-way express service remained west of Myrtle Avenue, for the M was switched to the local tracks at that time.

[31] On January 24, 1977, as part of a series of NYCTA service cuts to save $13 million, many subway lines began running shorter trains during middays.

The J was truncated to Queens Boulevard just after midnight on September 11, 1977,[33] and to 121st Street on April 15, 1985, as portions of the elevated Jamaica Line closed and were demolished.

[35] The new Z trains would go skip-stop between Jamaica Center and Broadway Junction (later extended to Myrtle Avenue) during rush hours, then making all J stops to Broad Street.

[38]: 7  Outer-zone expresses, after Crescent Street would skip stops on the local track until Eastern Parkway, from where it would run on the express track, stopping at Myrtle Avenue before going straight to Essex Street in Manhattan, skipping Marcy Avenue.

[38]: 7–8  To make J/Z service more attractive, all trains on those lines consisted of refurbished subway cars that were more quiet, graffiti-free, and had improved lighting and new floors.

[38]: 49 Queens Borough President Claire Schulman made multiple recommendations about revisions to the service plan for the extension at the MTA's February 1988 board meeting.

She recommended that trains should use the express track between Myrtle Avenue and Eastern Parkway to reduce travel times, and that the Chrystie Street Connection be reused for service to the Jamaica Line.

[52] The closure was anticipated to last until October 1999, but regular subway service was restored one month ahead of schedule.

[53] The project cost $130 million, including replacing the tracks support structure, signal system and other equipment.

[58] In May 2009, after the New York State Legislature passed legislation to offer financial support to the MTA, this planned service cut was taken off the table.

[64][65][66] In March 2020, skip-stop service was temporarily suspended due to lack of ridership and train crew availability caused by the COVID-19 pandemic.

[69][70] From December 29, 2021,[71][72] to January 19, 2022, skip-stop service was again suspended due to a shortage of crew members exacerbated by the COVID-19 pandemic.

Phase 3 will close down the Jamaica Center-bound platforms at Cypress Hills on July 22, 2024, and at 85th Street–Forest Parkway on August 12, 2024, for renovations until early 2025.