Nothing herein shall authorize the commissioner to proceed under the provisions of § 13a-5 and subsection (c) of § 13a-73 with any work pertaining to any such roads or bridges unless, under the Act of Congress or the federal grant allocating funds for such purpose, or by agreement with the government of the United States or any agency thereof, all costs and expenditures incurred in connection therewith shall be reimbursed by the government of the United States or such agency; and provided no commitments or expenditures of state funds shall be made by the commissioner except with the approval of the Governor.