Any state road general obligation bonds which are outstanding may at any time be refunded by the issuance of refunding bonds in an amount deemed necessary to refund the principal of the bonds to be refunded, together with any unpaid interest thereon; to accomplish the purpose of the amendment and to pay any premiums and commissions necessary to be paid in connection therewith. Any refunding may be effected whether the state road general obligation bonds to be refunded shall have then matured or shall thereafter mature. Any refunding bonds issued pursuant to this article shall be payable from the safe road bond debt service fund.