At least one year prior to the date any interest is due and payable on such bonds or before the maturity date of any such bonds, the state finance committee shall estimate, subject to the provisions of RCW 47.26.405, the percentage of the receipts in money of the motor vehicle fund, resulting from collection of excise taxes on motor vehicle fuels, for each month of the year which shall be required to meet interest or bond payments hereunder when due, and shall notify the state treasurer of such estimated requirement. The state treasurer shall thereafter from time to time each month as such funds are paid into the motor vehicle fund, transfer such percentage of the monthly receipts from excise taxes on motor vehicle fuels of the motor vehicle fund to the bond retirement fund, hereby created, which fund shall be available solely for payment of interest or bonds when due. If in any month it shall appear that the estimated percentage of money so made is insufficient to meet the requirements for interest or bond retirement, the treasurer shall notify the state finance committee forthwith and such committee shall adjust its estimates so that all requirements for interest and principal of all bonds issued shall be fully met at all times.