The South Busway is a two-lane bus rapid transit highway serving southern portions of the city of Pittsburgh.

Washington Transit Tunnel across the Monongahela River from Downtown Pittsburgh to the Overbrook neighborhood of the city, bypassing the crowded Pennsylvania Route 51 (Saw Mill Run Boulevard).

While light rail would be developed during the following decade, the Port Authority decided to use the corridor to allows buses to avoid the crowded, narrow, and stop light-filled Route 51.

The Yellow colored "Y" routes serve the length of the busway, entering and exiting at its southern terminus at Glenbury station.

Four local routes (39 Brookline, 40 Mt Washington, 41 Bower Hill, and 44 Knoxville) branch of off the busway to serve city neighborhoods.