Where it is apparent to the county board that a county or township road causes or would cause unnecessary burdens upon the county or township or upon the landowners adjoining such road, the county board may provide that such road may be fenced by such landowners; Provided, the safety and welfare of the traveling public are not substantially affected thereby; provided further, that the county board may install and maintain auto gates through such fences where the road crosses the fences; and provided further, that auto gates shall be not less than eighteen feet in length when located upon an established graded road.