181st Street is served by two New York City Subway lines; there is a 181st Street station at Fort Washington Avenue on the IND Eighth Avenue Line (A trains) and a 181st Street station at St. Nicholas Avenue on the IRT Broadway – Seventh Avenue Line (1 trains). The stations are about 500 metres (550 yd) from each other and are not connected. The George Washington Bridge Bus Terminal is a couple of blocks south on Fort Washington Avenue. 181st Street is also the last south/west exit in New York on the Trans-Manhattan Expressway (I-95), just before crossing the George Washington Bridge to New Jersey.

How many subway lines serve 181st Street?