36 Pa. Stat. § 670-906
Whenever there is a division of responsibility between the Commonwealth and any county, city, borough, town or township, for the construction or maintenance of any portion of the width of a public highway which forms a part of the State highway route, or the local authorities of such county, city, borough, town or township, are responsible for the construction or maintenance of structures which form a part thereof, it shall be lawful for the local authorities and the department to provide by agreement that the department may, in the discretion of the secretary, construct or maintain with its own forces the entire width of such highway or any structures forming a part thereof which are the responsibility of the local authorities. Such agreements shall provide for the reimbursement of the Commonwealth by the local authorities for any and all moneys expended by the department in the construction and maintenance of any structures or portions of the width of the highway for which the local authorities are responsible.
36 P.S. § 670-906