(a) Except as provided in this section, when the principal of, and interest on, all bonds issued under the authority of this chapter in connection with a particular tollway project shall have been paid, or the required provision made for their payment, and upon resolution of the authority involved filed with the city clerk of the city involved, that tollway project shall be and become part of the city's street system and shall thereafter be operated by the city free of tolls and charges.
(b) At the time of the final payment of principal and interest, or the making of adequate provision therefor, of outstanding revenue bonds with reference to a particular tollway project, the authority involved may determine and declare, by resolution entered in its records, that the tollway project involved is not to become part of the city street system, but is to continue to be operated. The tollway project revenues derived therefrom over and above expenses of maintenance, repair, and operation are to be pledged to and used for the payment of revenue bonds issued for financing the cost of another tollway project. However, no such pledge or use of tollway revenues for the payment of the principal and interest of bonds for any other tollway project shall be undertaken until the principal and interest of all outstanding bonds of the tollway project involved shall have been fully paid, or the required provision made for their payment.