53 Pa. Stat. § 15563
Whenever an operating company shall operate as one system street railway transit facilities, or any surface, underground, and/or elevated railways, under two or more separate franchises, such city may, if it so elect, condemn and take hereunder the property and franchises of any one or more companies which own or have an interest in such railways or in any of them, and which have, by lease or otherwise, surrendered to such operating company the possession and operation thereof, without at the same time condemning the interest of the operating company therein or the properties, facilities, and franchises of such operating company, to the intent that such city may, if it so elect, succeed to the rights, properties, facilities, and franchises of all lessor and/or underlying companies of such system of railways, exclusive of the rights, properties, facilities, and franchises of the operating company: Provided, however, That nothing herein contained shall prevent the taking and condemnation of the properties, facilities, and franchises of all the lessor and/or underlying companies, together with those of the operating company: And provided further, That the right to take and condemn hereunder motor buses, taxicabs, or trackless trolleys, owned by or controlled by such operating company through stock ownership or otherwise, shall be exercised only in case all other properties, facilities, franchises, and leaseholds of such operating company, used or useful in connection with the operation of transit facilities, are taken and condemned, but nothing herein contained shall affect the rights of such cities to acquire such motor buses, taxicabs, or trackless trolleys under the terms of any ordinance or ordinances relating thereto.
53 P.S. § 15563