Whenever the percentage of the motor vehicle fund arising from excise taxes on motor vehicle fuels payable into the bond retirement fund, 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 to reduce the requirements upon the fuel excise tax portion of the motor vehicle fund at the next interest or bond payment period.