(a) In a county that appoints one or more road superintendents, the commissioners court by contract may construct, grade, gravel, or otherwise improve a road or bridge.
(b) At the time the contract is made, the commissioners court shall direct the county treasurer to:
(1) transfer the amount of money stipulated in the contract to a particular fund; and
(2) keep a separate account of the money.
(c) The money may be used only for payment under the contract and may be paid only on the order of the commissioners court.