During rush hours, B service is extended north on the IND Concourse Line local tracks to Bedford Park Boulevard. B service only runs weekdays from 06:00 to 21:50. At other times, local service on the IND Eighth Avenue Line is provided by the C (A during late nights), express service on the IND Sixth Avenue Line is provided by the D, and service on the BMT Brighton Line in Brooklyn is provided by the Q. The B is one of only two New York City Subway services that have two or more stations with the same name (the other being the R train): It has two "Seventh Avenue" stations, one in Brooklyn (on Flatbush Avenue) and the other in Manhattan (on 53rd Street).
Subsequent to the opening of the Chrystie Street Connection the former BB trains were combined with the former T service of the BMT West End Line, creating a through service from Washington Heights to Coney Island. This service was initially to have been signed BT but was simply signed B instead.
The partial closure of the Manhattan Bridge to subway service between 1986 and 2004 affected B service by severing the connection between the northern and southern portions of the route. Beginning on April 26, 1986, the northern B (via Sixth Avenue, informally called "Orange B") and the southern B (via the BMT Broadway Line, informally called "Yellow B") operated as two different services. The Orange B more or less duplicated the former BB service, and the Yellow B imitated the old T service.
The former B service resumed December 11, 1988. On October 29, 1989, the IND 63rd Street Line opened, extending service to 21st Street–Queensbridge. B service ran through this new line on weekends. A year later, it would also run here on weekday evenings.
On July 22, 2001, B service over the Manhattan Bridge was again interrupted and service recast similarly to the 1986 changes. However, this time the West End Line portion of the run was redesignated as the W. B service ran weekdays only, to Bedford Park Boulevard during rush hours and 145th Street during middays and evenings.
On February 22, 2004, the Manhattan Bridge was fully reopened to subway service. B trains were extended through Grand Street station and over the north tracks of the Manhattan Bridge into Brooklyn, replacing the Q Diamond as the Brighton Express to Brighton Beach.
With this most recent service change, the only part of the original B service of 1940 that remains signed as B is the local service between 145th Street and 34th Street–Herald Square (not the other Penn Stations) in Manhattan.
The following table shows the lines used by Route B, with shaded boxes indicating the route at the specified times: