The board of commissioners on behalf of the special road districts, and the county commission on behalf of the townships, shall sell said bonds to the best advantage and the proceeds shall be paid over to the treasurer of the district or the county or township, as the case may be, and be by him disbursed, on the order of the board of commissioners or county commission, in payment of the cost of holding said election and in paying the cost of constructing or improving roads in such districts or townships, including bridges and culverts.