The Staten Island Railway is not officially considered part of the subway, as it lacks a rail link with the subway system, so passengers traveling between Staten Island and another borough must take the Staten Island Ferry or an MTA bus; free transfers are allowed to the subway and bus systems.
By annual ridership, the New York City Subway is the busiest rapid transit rail system in both the Western Hemisphere and the Western world, as well as the seventh busiest rapid transit rail system in the world; only the metro (subway) systems in Beijing, Shanghai, Seoul, Tokyo, Guangzhou, and Moscow record higher annual ridership.
Stations served by express trains are typically major transfer points or destinations.
and exhibited his idea for a subway propelled by pneumatic tube technology.
One of the more expansive proposals was the "IND Second System", part of a plan to construct new subway lines in addition to taking over existing subway lines and railroad rights-of-way.