The S service operates the Franklin Avenue Shuttle in Brooklyn.
The S is a special shuttle designation rather than a conventional numbered or lettered through-service. Its Franklin Avenue branch connects Franklin Avenue with Prospect Park, providing a short north–south link in central Brooklyn. The route is part of the B Division, which uses lettered services.
The Franklin Avenue Shuttle replaced the former Franklin Avenue Line’s through operation after service patterns changed. Today, it provides local access to neighborhoods and connections with the A, C, and Q services at different points along its route. It is distinct from the Rockaway Park Shuttle, which also uses the letter S but serves a separate geographic area in Queens.
A common mix-up is assuming that every S service refers to one continuous route. In the New York City Subway, shuttle services can share the same designation while operating on separate lines. The Franklin Avenue Shuttle is therefore identified by both its S designation and its Brooklyn route name.