The Center City Commuter Connection (CCCC), commonly referred to as "the commuter tunnel", is a passenger railroad tunnel in Center City, Philadelphia, Pennsylvania, United States, built to connect the stub ends of the two separate regional commuter rail systems, originally operated by two rival railroad companies: the Pennsylvania Railroad and the Reading Company. All of the SEPTA Regional Rail lines except for the Cynwyd Line pass completely through the four-track tunnel, which contains two underground stations, Suburban Station and Jefferson Station, and the above-ground upper-level concourse for the east–west commuter lines serving 30th Street Station. Planning and development Suburban Station, located at 16th Street and JFK Boulevard, was the underground terminus of the commuter rail lines of the Pennsylvania Railroad (PRR). The Reading Company (RDG) ran trains on an elevated approach above city streets into the Reading Terminal, located at 12th and Market Streets (one block west of where Jefferson Station was built). The connection, the first of its kind in the United States, was built to allow trains to run through Philadelphia's downtown central business district, by uniting the commuter lines of the two rail systems. R. Damon Childs was a junior land planner with the Philadelphia City Planning Commission when he proposed the CCCC to permit through-routing of the Pennsylvania Railroad and the Reading Railroad suburban lines. There already was a 0.8-mile (1.3 km) subway from 16th Street to 20th Street, a portion of the trackage connecting Suburban Station with 30th Street Station to the west. The tunnel project extended four of Suburban Station's eight tracks 1.7 miles (2.7 km) eastward. The proposed tunnel addition would pass just north of City Hall and then pass over the Broad Street Subway. The tracks would run under Filbert Street, would then curve to the north after 11th Street, pass under the Ridge Avenue Subway spur line, and run northward under 9th Street, ascending to join the Reading embankment near Spring Garden Street. Underground replacement for Reading Terminal—originally to be called 11th Street Station—was part of the Market East redevelopment project. At first the idea seemed preposterous because it required excavation under Philadelphia City Hall, one of the most massive buildings in the world, but it was nevertheless incorporated by Edmund N. Bacon into the city's 1960 Comprehensive Plan. Groundbreaking for the tunnel project was on June 22, 1978. It took six years to complete at a cost of $330 million