Bx15 and M125 buses

The Bx15 and M125 bus routes constitute the Third Avenue/125th Street Line, a public transit line in New York City. The Bx15 runs between Fordham Plaza and the Hub in the Bronx, running primarily along Third Avenue. The M125 runs between the Hub in the Bronx and Manhattanville in Manhattan, running along Willis Avenue in the South Bronx and along 125th Street in Harlem, Manhattan.

Prior to 2022, the corridor was a single bus route, the Bx15. The route is the successor to a streetcar line of the Union Railway Company and later the Third Avenue Railway known as the Willis Avenue Line or Willis Avenue−125th Street Line. The streetcar line, the first street railway in the Bronx, was known as the Harlem Bridge, Morrisania, and Fordham Railroad. The route began operation on Third Avenue in the Bronx in 1864, and the company was incorporated as the Union Railway Company in 1892. The Union Railroad applied in 1904 for extensions of several streetcar lines into Manhattan, including an extension of the Willis Avenue Line across 125th Street. The Willis Avenue Line was ultimately extended in 1916 across the 125th Street Crosstown Line.

The streetcar line was replaced by bus service in 1941; the route was known as the Bx29 prior to 1984. From 1973 to 2013 the Bx15 shared Third Avenue with the Bx55, a limited-stop service which replaced rapid transit service on the Third Avenue Elevated line between the Hub and Williamsbridge. In 2013, the Bx55 was converted into the Bx15 Limited, extending the route south to Manhattan, but eliminating service north of Fordham Plaza. The Bx15 south of the Hub was expected to be split into a new M125 bus route in 2020, but was delayed due to the COVID-19 pandemic in New York City; the split took place on June 26, 2022.