The money remaining in the toll revenue fund, after providing the amount required for interest and redemption of bonds, shall be held and applied as provided in the proceedings authorizing the issuance of the bonds. If the proceedings authorizing the issuance of the bonds do not require surplus revenues to be held or applied in any particular manner, they shall be allocated and used for such other purposes incidental to the acquisition, construction, operation, and maintenance of the toll tunnel as the authority determines.