When the road improvements have been completed and accepted, the roads shall constitute a part of the county road system and shall be maintained by the county. If the owners of more than fifty percent of the area in the district petition the board for maintenance in excess of that given other similar county roads, the board may levy and collect annually a special levy of not to exceed three and five-tenths cents on each one hundred dollars on all taxable property in the district subject to section 77-3443. The money as collected shall be credited to the rural road improvement district fund and used only for the repair and maintenance of the roads in the district.