When all bridge bonds issued under sections 5593.01 to 5593.24 of the Revised Code, in connection with any bridge and the interest thereon have been paid, or a sufficient amount for the payment of all such bonds and the interest thereon, to the maturity thereof has been set aside in trust for the benefit of the bondholders, such bridge shall become part of the state highway system, shall thereafter be maintained by the department of transportation, and shall be free of tolls.
R.C. §5593.23