BD, Bd or bd may refer to:
The B Sixth Avenue Express is a rapid transit service in the B Division of the New York City Subway. Its route emblem, or "bullet", is colored bright orange since it uses the IND Sixth Avenue Line in Manhattan. The B only operates on weekdays except nights. On middays and evenings, the B operates between 145th Street in Harlem, Manhattan and Brighton Beach in Brooklyn via Central Park West Local, the north side of the Manhattan Bridge, and Brighton Express. During rush hours, the B is extended to and from Bedford Park Boulevard in the Bronx via Concourse Local.
The designation B was originally intended to designate express trains originating in the Washington Heights neighborhood of Manhattan and operating in Midtown Manhattan on the IND Sixth Avenue Line. However, the original B service, beginning with the opening of the Sixth Avenue Line in 1940 and continuing until the opening of the Chrystie Street Connection in 1967, ran only as a rush-hour local between 168th Street – Washington Heights and 34th Street – Herald Square. This service was designated BB in conformance with Independent Subway System protocol of using double letters to indicate local services.