(a) The commission by order may authorize the issuance of toll revenue bonds to pay all or part of the cost of a toll project or system. The proceeds of a bond issue may be used solely for the payment of the project or system for which the bonds were issued and may not be divided between or among two or more projects. Each project is a separate undertaking, the cost of which shall be determined separately.
(b) As determined in the order authorizing the issuance, the bonds of each issue shall:
(1) be dated;
(2) bear interest at the rate or rates provided by the order and beginning on the dates provided by the order and as authorized by law, or bear no interest;
(3) mature at the time or times provided by the order, not exceeding 40 years from their date or dates; and
(4) be made redeemable before maturity, at the price or prices and under the terms provided by the order.

(c) The commission may sell the bonds at public or private sale in the manner and for the price it determines to be in the best interest of the department.
(d) The proceeds of each bond issue shall be disbursed in the manner and under the restrictions, if any, the commission provides in the order authorizing the issuance of the bonds or in the trust agreement securing the bonds.
(e) If the proceeds of a bond issue are less than the toll project or system cost, additional bonds may be issued in the same manner to pay the costs of a project or system. Unless otherwise provided in the order authorizing the issuance of the bonds or in the trust agreement securing the bonds, the additional bonds are on a parity with and are payable, without preference or priority, from the same fund as the bonds first issued. In addition, the commission may issue bonds for a project or system secured by a lien on the revenue of the project or system subordinate to the lien on the revenue securing other bonds issued for the project or system.
(f) If the proceeds of a bond issue exceed the cost of the toll project or system for which the bonds were issued, the surplus shall be segregated from the other money of the commission and used only for the purposes specified in the order authorizing the issuance.
(g) In addition to other permitted uses, the proceeds of a bond issue may be used to pay costs incurred before the issuance of the bonds, including costs of environmental review, design, planning, acquisition of property, relocation assistance, construction, and operation.
(h) Bonds issued and delivered under this subchapter and interest coupons on the bonds are a security under Chapter 8, Business & Commerce Code.
(i) Bonds issued under this subchapter and income from the bonds, including any profit made on the sale or transfer of the bonds, are exempt from taxation in this state.