Pending final redemption of bond or bonds for improving the road, roads, highway, or street, the county treasurer is hereby authorized to invest such sinking fund in interest-bearing time certificates of deposit in depositories approved and authorized to receive county money, but in no greater amount in any depository than the same is authorized to receive deposits of county funds; and the interest arising from such certificate of deposit shall be credited to its respective sinking fund as provided by sections 39-1601 to 39-1636.