Transit Expressway Revenue Line

The Transit Expressway Revenue Line (TERL), commonly known as Skybus, was a proposed people mover rapid transit system developed by Westinghouse for the city of Pittsburgh, Pennsylvania during the 1960s–1970s. In contrast to the traditional streetcars then in use, the technology used a dedicated elevated concrete track and rubber-tired driverless cars.

A demonstration of the Skybus technology was installed at the Allegheny County Fairgrounds in 1965, and operated as a visitor attraction during the Allegheny County Fair until 1971. Plans for an operational Skybus system in Pittsburgh, including a connection from Downtown Pittsburgh to the South Hills via the Wabash Tunnel, were rejected in the 1970s.

While the Skybus proposal in Pittsburgh failed, the Skybus technology was developed into the Innovia APM, which is in service across the world. A preserved Skybus vehicle is on display at the Innovia APM manufacturing facility in West Mifflin, which is now operated by Alstom.