Exclusive jurisdiction in and over the aforesaid parcel of land is hereby ceded to the United States of America by the Commonwealth of Pennsylvania for the erection of forts, magazines, arsenals, dock yards and other needful buildings, to be used by the United States for military and other public purposes, with the exception of roads abutting on the said land which are not already under the jurisdiction of the United States.
74 P.S. § 115.2