Whenever the percentage of the motor vehicle fund arising from excise taxes on motor vehicle and special fuels payable into the transportation improvement board bond retirement account, shall prove more than is required for the payment of interest on bonds when due, or current retirement of bonds, any excess may, in the discretion of the state finance committee, be available for the prior redemption of any bonds or remain available in the fund [account] to reduce the requirements upon the fuel excise tax portion of the motor vehicle fund at the next interest or bond payment period.