These tracks are a vestige of New York City's first electric crosstown cable railway line, from Harlem to Manhattanville. On August 25, 1885, the city's first electric cable car ran up 10th Avenue from West 125th Street in Manhattanville to Highbridge. The line was constructed by the 3rd Avenue Railway Company as an experiment. Cleaner and faster than horse cars, the cable car's successful trial run persuaded the company to introduce the system into its eight miles of 3rd Avenue track from the Harlem River to City Hall.
The square plates between the tracks bearing the identification "3rd Ave RR"--although located on 12th Avenue at 125th Street--recall this as part of the vast network of surface lines that belonged to the 3rd Avenue Railway Company, once the richest railway company in the country. They are a serendipitous window on the city's transportation history and its corporate history (inasmuch as controversy often surrounded the means by which this and other street railway companies received land grants). By extension, the tracks are also a window on African-American civil rights history: in 1855, a successful suit against the 3rd Avenue Railway Company resulted in the desegregation of New York City's public cars.