What does “IRT” stand for in the history of the New York City Subway?

“IRT” stands for Interborough Rapid Transit, the company that operated New York’s first subway line.

The Interborough Rapid Transit Company was incorporated in 1902 and built the first underground subway route under contracts with New York City. Its first section opened in 1904, connecting City Hall with Harlem. The company also operated several elevated and subway extensions as the network expanded.

The IRT used narrower cars and platforms than the later BMT and IND systems. This difference is why the modern subway is commonly described as having separate A Division and B Division equipment. Numbered routes generally descend from the former IRT network, while lettered routes mostly developed from the BMT and IND systems.

The IRT’s corporate identity disappeared after New York City took over the private subway companies in 1940. Nevertheless, the abbreviation remains essential historical terminology. Lines such as the Lexington Avenue, Broadway–Seventh Avenue, and Flushing lines contain major portions of the former IRT system.