(a) Just compensation shall be paid upon the removal of any outdoor advertising device (1) lawfully in existence on the effective date of this act; (2) lawfully on any highway made a part of the interstate or primary system on or after the effective date of this act; or (3) otherwise lawfully erected on or after the effective date of this act.

(b) Just compensation shall consist of payment for (1) the taking from the owner of an outdoor advertising device of all right, title, leasehold and interest in such outdoor advertising device, and (2) the taking from the owner of the real property on which an outdoor advertising device is located of the right to erect and maintain such outdoor advertising device.

(c) The department shall require removal of all nonconforming outdoor advertising devices lawfully on any highway made a part of the interstate or primary system on or after the effective date of this act no later than the end of the sixth year after the said highway is made a part of the interstate or primary system.

(d) Notwithstanding the provisions of subsections (b) and (c) of this section, the periods specified therein within which the department shall require removal of all nonconforming outdoor advertising devices may be extended, if necessary, until such time as Federal funds are available to reimburse the Commonwealth for the Federal share of the costs of removal of those signs for which Federal contribution is provided in section 131 of Title 23 of the United States Code.