A section of the Chicago-Philadelphia Main Line (now part of Amtrak's Keystone Corridor) was electrified in 1915. The suburban service runs between the former Broad Street Station in Philadelphia and the village of Paoli. The PRR electrification utilized overhead catenary wires electrified at , and was fed by four substations in Arsenal, West Philadelphia, Bryn Mawr, and Paoli. It was expanded in 1919 on the PRR's Chestnut Hill line, and in the 1920s on the Philadelphia-Washington, D.C. main line between Philadelphia and Wilmington, and on the West Chester Line between Philadelphia and West Chester, with the latter two lines being fed through a single substation located in Chester.