53 Pa. Stat. § 25496
In case any property is damaged by the construction of such subway or tunnel, or in case any such city desires to enter upon any land to make any investigation, or desires to take, use, or appropriate the fee or any lesser estate in any lands or properties necessary for the construction of such subway or tunnel, and is unable to agree with the owner or owners upon the price to the paid therefor, the damages caused by such construction shall be ascertained and collected in the same manner as is now or may hereafter be provided by law for ascertaining and collecting damages to abutting properties, caused by the grading or otherwise improving of streets in such cities; and the damages caused by such entry or taking, using and appropriation, of land, shall be ascertained and collected in the same manner as is now or may hereafter be provided by law for ascertaining and collecting damages for the taking, occupation, or injury of property necessary in the laying out, opening, widening, and grading of streets in the municipal corporations of this Commonwealth.
53 P.S. § 25496