53 Pa. Stat. § 15562
It shall be lawful for, and the right is hereby conferred upon, any city of the first class to condemn, enter upon, take, appropriate, occupy, and use street railway transit facilities, together with the property and franchises of any individual, partnership, corporation, or other artificial person, owning, leasing, or operating street, underground, or elevated passenger railways, motor buses, taxicabs, or trackless trolleys, situated or operated principally within such city, together with the properties and franchises of any subsidiary of any such owner. The term "street railway transit facilities," as used in this act, includes every railroad and railway, by whatsoever power operated, or any extension or extensions thereof, for public use in the conveyance of passengers and property or both, being mainly located upon, over, above, below, across, through, or along any street, avenue, road, highway, bridge, or public place, and the facilities, plant, and equipment thereof, including tunnels, subways, bridges, elevated structures, tracks, poles, wires, conduits, power houses, sub-stations, lines for the transmission of power, car barns, shops, yards, sidings, turnouts, switches, stations, and approaches thereto, cars and motive equipment, and all works, buildings, appliances, and appurtenances, necessary and convenient for the proper construction, equipment, maintenance, and operation of such railroad or railway: Provided, however, That there shall be excluded from any such condemnation or taking stocks, bonds, and other securities and property owned by such individual, partnership, corporation, or other artificial person, not used or useful in connection with the operation of the said transit facilities: And provided further, That whenever an operating company shall operate as one system, whether as owner, lessee, operating agent, or otherwise, any such transit facilities under two or more separate franchises, it shall be lawful for any such city to condemn or take hereunder the properties, facilities, and franchises, or any of them, pertaining to or operated under any one or more separate franchises, without at the same time condemning and taking all of the properties, facilities, and franchises, as hereinabove defined, pertaining to the entire system.
53 P.S. § 15562