In total, 40% of track is not underground despite the "subway" moniker.
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.
In 1912, workers excavating for the present-day BMT Broadway Line dug into the old Beach tunnel; today, no part of this line remains as the tunnel was completely within the limits of the present day City Hall Station under Broadway.
By the time the first subway opened, the lines had been consolidated into two privately owned systems, the Brooklyn Rapid Transit Company (BRT, later Brooklyn–Manhattan Transit Corporation (BMT)) and the Interborough Rapid Transit Company (IRT).
Opened in 1904, the New York City Subway is one of the world's oldest public transit systems, one of the world's most used metro systems, and the metro system with the most stations and the most trackage.
Stations are located throughout the boroughs of Manhattan, Brooklyn, Queens, and the Bronx.