Until 1976, the Jamaica Line (over Broadway west of East New York) was also served by the KK Broadway Brooklyn Local (K after 1973), which ran to 57th Street (IND Sixth Avenue Line) via the Chrystie Street Connection after 1968. This was the successor to the original BMT Canarsie Line service, which ran full-time until the 14th Street–Eastern Line was completed to East New York in 1928.
The second major service on the Broadway Elevated ran between Canarsie and Williamsburg via the BMT Canarsie Line, started on July 30, 1906 when the Broadway and Canarsie tracks were connected at East New York. As part of the Dual Contracts, an extension from Cypress Hills east to Jamaica was completed on July 3, 1918, a third express track was added west of East New York, and express trains began running in 1922.
The Brooklyn–Manhattan Transit Corporation numbered its services in 1924, and the Canarsie and Jamaica services became 14 and 15. Both ran express during rush hours in the peak direction west of East New York, and additional 14 trains, between Eastern Parkway (now Broadway Junction) or Atlantic Avenue on the Canarsie Line and Manhattan provided rush-hour local service on Broadway. When the 14th Street–Eastern Line and Canarsie Line were connected on July 14, 1928, the old Canarsie Line service was renamed the Broadway (Brooklyn) Line, providing only weekday local service over the Broadway Elevated west of Eastern Parkway. The Atlantic Avenue trips remained, and rush-hour trains continued to serve Rockaway Parkway (Canarsie), though they did not use the Broadway express tracks. The 14 was later cut back to only rush-hour service.
On the Manhattan end, the first extension was made on September 16, 1908, when the Williamsburg Bridge subway tracks opened. Broadway and Canarsie trains were extended to the new Essex Street terminal, and further to Chambers Street when the line was extended on August 4, 1913. When the BMT Nassau Street Line was completed on May 30, 1931, the 15 was extended to Broad Street, and the 14 was truncated to Canal Street. Some 14 trains began terminating at Crescent Street on the Jamaica Line in 1956.
Inbound morning rush hour skip-stop service between Jamaica and East New York was implemented on June 18, 1959. Express 15 trains served "A" stations, while the morning 14 became the Jamaica Local, running between Jamaica and Canal Street, and stopped at stations marked "B". These stations were as follows:
Letters were assigned to most BMT services in the early 1960s. The 15 became the J (express) and JJ (local), and the 14 became the KK.
The next change was made on July 1, 1968, when the Chrystie Street Connection tracks to the Williamsburg Bridge opened. The Jamaica Line portion of the rush-hour JJ was modified to become a new rush-hour KK, running between Jamaica (peak direction) or Eastern Parkway (both directions) and the new 57th Street station on the IND Sixth Avenue Line in Manhattan. The RJ was eliminated, being cut back to an RR variant, and the off-hour JJ was relabeled QJ (but not extended to Brighton Beach). At the same time, the existing skip-stop service was extended to afternoon Jamaica-bound trains, with those QJ trains running express west of Eastern Parkway and service "A" stations east to Jamaica, and those KK trains serving "B" stations. Less than two months later, on August 18, the QJ was extended to Coney Island–Stillwell Avenue.
These new services were slowly eliminated in the 1970s due to financial problems. First, on January 2, 1973, the QJ was cut back full-time to Broad Street and renamed the J; the M was extended to Coney Island in its place. At the same time, the KK was cut back to Eastern Parkway and renamed the K, and both skip-stop patterns were carried out by alternate J trains. But that was not enough; the K was discontinued on August 30, 1976, eliminating the J skip-stop and express service east of Myrtle Avenue. (One-way express service remained west of Myrtle Avenue, since the M was switched to the local tracks at that time.)
The following table summarizes the changes that were made between 1959 and 1976.
| Morning rush-hour local | Morning rush-hour express | Afternoon rush-hour local | Afternoon rush-hour express | Other local | Other service | |
|---|---|---|---|---|---|---|
| 1959-67 | 14/KK 168th Street - Canal Street, "B" stops inbound | 15/J 168th Street - Broad Street, "A" stops inbound | 14/KK Crescent Street, Atlantic Avenue, or Rockaway Parkway - Canal Street | 15/J 168th Street - Broad Street | 15/JJ 168th Street - Broad Street | |
| 1967-68 | JJ 168th Street - Canal Street, "B" stops inbound | QJ 168th Street - Brighton Beach, "A" stops inbound | JJ Crescent Street or Atlantic Avenue - Canal Street | QJ 168th Street - Brighton Beach | JJ 168th Street - Broad Street QJ 168th Street - Brighton Beach, middays and early evenings | RJ 168th Street - Brooklyn, rush hour non-peak direction only |
| 1968-1973 | KK 168th Street - 57th Street, "B" stops inbound | QJ 168th Street - Brooklyn, "A" stops inbound | KK 168th Street - 57th Street, "B" stops outbound | QJ 168th Street - Brooklyn, "A" stops outbound | QJ 168th Street - Broad Street or Brooklyn | |
| 1973-1976 | K Eastern Parkway - 57th Street | J 168th Street - Broad Street, two inbound patterns, one for "A" stops and one for "B" stops | K Eastern Parkway - 57th Street | J 168th Street - Broad Street, two outbound patterns, one for "A" stops and one for "B" stops | J 168th Street - Broad Street |
The J was truncated to Queens Boulevard just after midnight on September 11, 1977, and to 121st Street on April 15, 1985, concurrent with the cutting-back of the Jamaica Line. The BMT Archer Avenue Line (subway section in Jamaica, Queens) opened on December 11, 1988, extending the line back east from 121st Street, and the present J/Z skip-stop pattern was implemented.
In 1990, weekend service terminated at Canal Street, but was then extended back to Chambers Street in 1994.
From April 30 to September 1, 1999, the Williamsburg Bridge was closed for reconstruction. J trains ran only between Jamaica Center-Parsons Archer and Myrtle Avenue. J/Z skip-stop service was in both directions between Jamaica Center and Eastern Parkway-Broadway Junction.
After September 11, 2001, service was suspended. J trains were extended beyond Broad Street via the BMT Montague Street Tunnel to replace the R to Bay Ridge-95th Street at all times except late nights, when it only ran to Broad Street and a shuttle ran in Brooklyn between 95th and 36th Streets. J/Z skip-stop service was suspended. During this time, the J was the longest local line in the system. Normal service on all three lines was restored on October 28.