The D 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 orange, since it uses the IND Sixth Avenue Line in Manhattan. The D operates at all times between 205th Street in Norwood, Bronx, and Stillwell Avenue in Coney Island, Brooklyn via Grand Concourse in the Bronx, Central Park West and Sixth Avenue in Manhattan, the north side of the Manhattan Bridge, and Fourth Avenue and West End in Brooklyn. During daytime hours, the D runs express between 145th Street in Manhattan and 36th Street–Fourth Avenue in Brooklyn and local elsewhere. During rush hours in the peak direction, the D also runs express between Fordham Road in the Bronx and 145th Street in Manhattan. Overnight D service is only express in Manhattan and local elsewhere. In its early years, the D ran to World Trade Center in Lower Manhattan via the lower IND Eighth Avenue Line. From 1954 to 1967, the D ran via the IND Culver Line to Coney Island. With the completion of the Chrystie Street Connection, service was rerouted via the BMT Brighton Line, running there from 1967 to 2001. A short-lived yellow D service ran via the BMT Broadway Line in Manhattan to the Brighton Line in Brooklyn, while orange D service used the Sixth Avenue, Central Park West, and Concourse Lines in Manhattan and the Bronx. From Wikipedia
