The department of transportation may operate such ferry system, including all operations, whether intrastate or international, upon any route or routes, as a revenue producing undertaking, and the State covenants with the holders from time to time of bonds issued pursuant to this chapter that so long as any of the bonds are outstanding and unpaid the State will continue to maintain and operate the ferry system and to impose and collect rates, rentals, and charges for the services, facilities, and commodities sold, furnished, or supplied through the facilities of the ferry system which will provide gross revenues sufficient to pay the principal of and interest on all bonds issued pursuant to this chapter, including reserves therefor, and to maintain all funds or reserves created pursuant to the certificate authorizing such bonds for the rehabilitation, renewal, and replacement of the facilities of the ferry system so as to maintain the same in good operating condition. The department shall have full charge of the construction, rehabilitation, rebuilding, enlarging, improving, and maintenance of the ferry system, including approaches and roadways incidental thereto that may be authorized by the department, the granting of concessions, the collection of tolls, and other charges for the services and facilities of the undertaking; provided that the department shall comply with the provisions of chapter 102 relating to contracts for concessions on public property. The gross revenues derived from the operation of the ferry system shall be appropriated, applied, or expended for the purposes and in the order of priority set forth in section [ 39-62 ]; provided that if the certificate authorizing the issuance of the bonds shall so provide, the revenues shall be appropriated, applied, or expended for the rehabilitation, renewal and replacement of the facilities required to maintain the ferry system in good operating condition, including such reserve or reserves therefor as shall be provided in the certificate, immediately after being appropriated, applied, or expended to the payment of the bonds and interest thereon, including reserves therefor, and before being appropriated, applied, or expended to the other purposes set forth in the section.