All moneys paid into the county treasury under a commutation road tax shall be kept separate and apart from the general county fund and, except as otherwise herein directed, shall be exclusively applied by the governing body of the county to repairing the highways and bridges of the county, by contract or otherwise, as may be deemed most expedient. The governing body of any county may use, for other county purposes than repairs of highways, any balance of the road commutation tax remaining in the county treasurer’s hands on the first day of January in each year.