The Abandoned Project : Lost But Found Season 1 - Episode 1 - The 9th Avenue Elevated Line

The IRT Ninth Avenue Line, often called the Ninth Avenue Elevated or Ninth Avenue El, was the first elevated railway in New York City. It opened in July 1868 as the West Side and Yonkers Patent Railway, as an experimental single-track cable-powered elevated railway from Battery Place, at the south end of Manhattan Island, northward up Greenwich Street to Cortlandt Street. By 1879 the line was extended to the Harlem River at 155th Street. It was electrified and taken over by the Interborough Rapid Transit Company in 1903.
The main line ceased operation in June 1940, after it was replaced by the IND Eighth Avenue Subway which had opened in 1932. The last section in use, over the Harlem River, was known as the Polo Grounds Shuttle. It closed in August 1958. This portion used a now-removed swing bridge called the Putnam Bridge, and went through a still-extant tunnel with two partially underground stations.
The line had the worst accident in the history of New York City elevated railways, on September 11, 1905, when a train derailed and fell to the street. There were 61 casualties.
Most of the line was closed June 11, 1940, and dismantled, following the purchase of the IRT by the City of New York. A small portion of the line north of 155th Street remained in service as the "Polo Grounds Shuttle". Service ended in August 1958 as a result of the departure of the New York Giants baseball team, which had relocated to San Francisco, and the ending of passenger service on the New York Central's Putnam Division.