The B Division uses lettered New York City Subway routes rather than numbered routes.
Its routes include the A, C, E, B, D, F, M, G, J, Z, L, N, Q, R, and W services. The division consists largely of lines built or operated by the former Brooklyn–Manhattan Transit Corporation and the Independent Subway System, commonly called BMT and IND lines.
The A Division uses numbered routes, including the 1, 2, 3, 4, 5, 6, 7, and 7 diamond services. B Division trains are generally wider and longer than A Division trains, so the two groups cannot freely use every track and station platform interchangeably.
The distinction is operational rather than a simple statement about boroughs or neighborhoods. Both divisions serve Manhattan, Brooklyn, Queens, and the Bronx. Staten Island Railway is separately classified and is not simply another lettered subway division.