Center City Commuter Connection

The Center City Commuter Connection (CCCC), commonly referred to as "the commuter tunnel", is a passenger railroad tunnel in Center City Philadelphia, Pennsylvania. The tunnel was built to connect the stub ends of the two separate regional commuter rail systems, which were originally operated by the Pennsylvania Railroad and the Reading Company, two rival rail companies. 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.

Tunnel data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).