The 149th Street Tunnel carries the train of the New York City Subway

New York City Subway

The New York City Subway is a rapid transit system owned by the City of New York and leased to the New York City Transit Authority, a subsidiary agency of the Metropolitan Transportation Authority and also known as MTA New York City Transit...

 under the Harlem River

Harlem River

The Harlem River is a navigable tidal strait in New York City, USA that flows 8 miles between the Hudson River and the East River, separating the boroughs of Manhattan and the Bronx...

 between the boroughs

Borough (New York City)

New York City, one of the largest cities in the world, is composed of five boroughs. Each borough now has the same boundaries as the county it is in. County governments were dissolved when the city consolidated in 1898, along with all city, town, and village governments within each county...

 of Manhattan and The Bronx. It runs directly beneath the 145th Street Bridge

145th Street Bridge

The 145th Street Bridge, located in New York City, USA, is a four-lane swing bridge that crosses the Harlem River, connecting 145th Street and Lenox Avenue in Manhattan with East 149th Street and River Avenue in the Bronx. It once carried northbound New York State Route 22 and New York State Route...

. Built from 1904–1905, the tunnel is part of the original IRT

Interborough Rapid Transit Company

The Interborough Rapid Transit Company was the private operator of the original underground New York City Subway line that opened in 1904, as well as earlier elevated railways and additional rapid transit lines in New York City. The IRT was purchased by the City in June 1940...

subway system.

Construction

The portion of the tunnel directly under the river is constructed of twin single-track cast-iron cylinders 16 feet in diameter, both lined with and buried in concrete. The approaches on either end are a double-track concrete arch structure.