Pittsburgh PA: View of the Knoxville Street Car (Trolley) emerging from the Mount Washington Tunnel into the South Hills Junction. In the early 1960s, Pittsburgh had the largest surviving streetcar system in the United States. The Pittsburgh Railways Company operated more than 600 PCC cars on 41 routes. In 1964 the system was acquired by the Port Authority of Allegheny County, which rapidly converted to buses. By the early 1970s, only a handful of streetcar routes remained, most of which used the Mt. Washington Tunnel just south of the Monongahela River to reach the South Hills area.