(a) The commissioners court may set aside from the bond proceeds:
(1) money to pay interest on the bonds; and
(2) money in the amount the commissioners court estimates to be required for operating expenses until the parking facility becomes sufficiently operational.
(b) The commissioners court may not set aside money under this section in an amount that exceeds the amount of money necessary to cover interest and operating expenses for the estimated period of construction and the first two years of operation, less any earnings during that time.