129th Street was a massive station on the IRT Third Avenue Line

IRT Third Avenue Line

The IRT Third Avenue Line, commonly known as the Third Avenue El, was an elevated railway in Manhattan and the Bronx, New York City. Originally operated by an independent railway company, it was acquired by the Interborough Rapid Transit Company and eventually became part of the New York subway...

, shared by trains of both the Third Avenue Line and IRT Second Avenue Line

IRT Second Avenue Line

The IRT Second Avenue Line, also known as the Second Avenue El, was an elevated railway in Manhattan, New York City, United States, operated by the Interborough Rapid Transit Company until city takeover in 1940...

 in the New York City Subway system. The next stop to the north was 133rd Street

133rd Street (IRT Third Avenue Line)

133rd Street was a station on the IRT Third Avenue Line. It was the first stop in the Bronx after crossing the Harlem River. It had two tracks and one island platform. It was served by trains of both the Third Avenue Line and IRT Second Avenue Line until June 11, 1940. The next stop to the north...

. The next stop to the south was 125th Street

125th Street (IRT Third Avenue Line)

125th Street was a station on the demolished IRT Third Avenue Line. It opened on December 30, 1878, and had three tracks and two levels. The lower level was built first and had two tracks and two side platforms for local trains. The upper level, built as part of the Dual Contracts, had one track...

 for Third Avenue Line trains and 125th Street

125th Street (IRT Second Avenue Line)

125th Street was a station on the demolished IRT Second Avenue Line. It had three tracks and two island platforms. The next stop to the north was 129th Street for terminating trains and 133rd Street for through trains. The next stop to the south was 121st Street for local trains and 86th Street for...

for Second Avenue Line trains. The station closed on May 12, 1955; however, the Second Avenue Line stopped serving it on June 11, 1940. 129th Street was the terminal for some trains, specifically those of the Second Avenue Line, which used the southernmost island platform.