History: The New York City Subway, United States

Many lines and stations have both express and local services. These lines have three or four tracks. Normally, the outer two are used for local trains while the inner one or two are used for express trains. Stations served by express trains are typically major transfer points or destinations. The BMT Jamaica Line uses skip-stop service on portions, where two services (J Z trains) operate over the line during rush hours and many stations are only served by one of the two.
History
A demonstration for an underground transit system in New York City was first built by Alfred Ely Beach in 1869. His Beach Pneumatic Transit only extended 312 feet (95 m) under Broadway in Lower Manhattan and exhibited his idea for a subway propelled by pneumatic tube technology. The tunnel was never extended for political and financial reasons, although extensions had been planned to take the tunnel southward to The Battery and northwards towards the Harlem River. The Beach subway was demolished when the BMT Broadway Line was built in the 1910s; thus, it was not integrated into the New York City Subway system.