The commission shall fix, charge and collect tolls for transit through the tunnel, and such tolls shall be so fixed and adjusted as to provide a fund sufficient to pay the bonds and the interest thereon and to provide an additional fund to pay the cost of maintaining, repairing and operating the tunnel. Such tolls shall not be subject to supervision or regulation by any state commission, board, bureau or agency. The tolls from the tunnel, except such part thereof as may be necessary to pay such cost of maintaining, repairing and operating, shall be set aside each month in a sinking fund, which is hereby pledged to, and charged with the payment of, (a) the interest upon such bonds as such interest shall fall due, (b) the necessary fiscal agency charges for paying bonds and interest, and (c) the payment of the bonds as they fall due, or, if all bonds mature at one time, the proper maintenance of a sinking fund sufficient for the payment thereof at such time, and (d) a margin for the payment of premiums upon bonds retired by call or purchase as herein provided. Such sinking fund shall be a fund for all such bonds without distinction or priority of one over another. Prior to the issuance of the bonds, the commission may provide, by resolution or by such trust indenture, for the use of the sinking fund, or any part thereof, in the purchase of any of the outstanding bonds, payable therefrom, at the market price thereof, but not exceeding the price, if any, at which the same shall at the next interest date be payable or redeemable, and all bonds so redeemed or purchased shall forthwith be canceled and shall not again be issued. The moneys in the sinking fund, less a reserve for payment of not exceeding one year’s interest on the bonds, if not used within a reasonable time for the purchase of bonds for cancellation as above provided, shall be applied to the redemption of bonds by lot at the redemption price then applicable.