How many subways systems are there in the world?

The Rapid Transit systems of the metropolitan areas of the following 14 U.S. cities include underground service. They are listed in chronological order by when their first underground service began.

• Boston, Massachusetts - 1 September 1897
• New York, New York - 27 October 1904
• Philadelphia, Pennsylvania - 1906
• Newark, New Jersey - 26 May 1935 *
• Chicago, Illinois - 17 October 1943
• Cleveland, Ohio - 15 March 1955
• San Francisco, California - 11 September 1972
• Washington, District of Columbia - 27 March 1976
• Atlanta, Georgia - 30 June 1979
• Baltimore, Maryland - 21 November 1983
• Pittsburgh, Pennsylvania - 15 April 1984
• Buffalo, New York - 1984
• Los Angeles, California - 14 July 1990
• Seattle, Washington - 15 September 1990 (rail service added in 2007)

* The Port Authority Trans-Hudson (PATH), a service connecting New York City and Newark, New Jersey via a rail tunnel under the Hudson River, began service on 25 February 1908.

The first transportation tunnel in the United States was the Auburn Tunnel. It was a canal tunnel near Auburn, Pennsylvania built for the Schuylkill Canal. It was opened in 1821 and closed in 1857.