(a) The commissioners court of a county may purchase through the comptroller road machinery and equipment, tires, and tubes to be used by the county.
(b) The commission must purchase an item under this section on competitive bids and in accordance with any rules of the commission.
(c) A purchase under this section must be made on the requisition of the commissioners court. When the court sends the requisition to the commission, the court must include with the requisition a general description of the item desired and a certification of the funds available to pay for the item.
(d) The commission may adopt rules to carry out the purpose of this section.