All funds deposited to the credit of the safe road bond debt service fund shall be kept by the treasurer of the state in a separate account and all money belonging to the fund shall be deposited in the treasury to the credit of the fund.
The fund shall be applied by the treasurer of the state for payments on the principal and interest on bonds sold pursuant to this article as it becomes due and payable. The remainder of the fund, if any, shall be invested by the state Board of Investments in the manner authorized under article six, chapter twelve of this code.