(a) All revenues of the bridge or ferry not required under the provisions of this chapter to be paid into the sinking fund provided in the resolution authorizing the issuance of bonds shall be paid into an operation and maintenance fund and be used by the State Highway Commission in the operation and maintenance of the bridge or ferry.
(b) However, all moneys in any operation and maintenance fund in excess of an amount deemed by the commission sufficient for operation and maintenance for an ensuing period of not less than twelve (12) months shall be paid into the sinking fund.