The S route serves the New York City Subway’s 42nd Street Shuttle.
The shuttle runs between Times Square–42nd Street and Grand Central–42nd Street in Manhattan. It uses the former east–west segment of the original IRT route and provides a short cross-Midtown connection beneath 42nd Street.
On subway maps and signs, shuttle services are identified by the letter S rather than by a conventional numbered or lettered through route. The S designation is also used for other shuttle services, so the route label by itself does not identify every shuttle in the system. The destination names do that work.
The 42nd Street Shuttle was created after through service along 42nd Street was replaced by the newer Lexington Avenue alignment. Its short length makes it one of the easiest routes to overlook, but it carries passengers between two of Manhattan’s busiest transit hubs and connects with numerous subway services.