Keystone Corridor

The Keystone Corridor is a 349-mile (562 km) railroad corridor between Philadelphia and Pittsburgh, Pennsylvania, that consists of two rail lines: Amtrak and SEPTA's Philadelphia-to-Harrisburg main line, which hosts SEPTA's Paoli/Thorndale Linecommuter rail service, and Amtrak's Keystone Service and Pennsylvanianinter-city trains; and the Norfolk SouthernPittsburgh Line. The corridor was originally the Main Line of the Pennsylvania Railroad.

Amtrak runs two intercity rail services along the Keystone Corridor: the Harrisburg-to-New York CityKeystone Service and the Pittsburgh-to-New York City Pennsylvanian. SEPTA operates daily Paoli/Thorndale commuter rail service between Philadelphia and Thorndale on the Philadelphia-to-Harrisburg main line. The towns along this stretch form a socio-cultural region called the "Philadelphia Main Line".

The tracks from Pittsburgh to Harrisburg are owned and maintained by Norfolk Southern, which acquired them from Conrail. They include the Horseshoe Curve west of Altoona. The tracks between Harrisburg and Philadelphia are owned and maintained by Amtrak, and are the only part of the Keystone Corridor that is electrified. The tracks join the Northeast Corridor at Zoo Interlocking near the Philadelphia Zoo and 30th Street Station.