[3] It opened following more than twenty years of public debate on the merits of subways versus the existing elevated rail system and on various proposed routes.

[4] Founded on May 6, 1902, by August Belmont, Jr., the IRT's mission was to operate New York City's initial underground rapid transit system after Belmont's and John B. McDonald's Rapid Transit Construction Company was awarded the rights to build the railway line in 1900, outbidding Andrew Onderdonk.

In 1913, as a result of massive expansion in the city, the IRT signed the Dual Contracts with Brooklyn Rapid Transit (BRT) in order to expand the subway.

[8] The IRT ceased to function as a privately held company on June 12, 1940, when its properties and operations were acquired by the City of New York.

(of the East and Harlem Rivers, from south to north) Several pieces of pre-unification IRT equipment have been preserved in various museums.