Tex. Transportation Code § 370.113

(a) The principal of, interest on, and any redemption premium on bonds issued by an authority are payable solely from:

(1) the revenue of the transportation project for which the bonds are issued;

(2) payments made under an agreement with the commission, the department, or other governmental entity as authorized by this chapter;

(3) money derived from any other source available to the authority, other than money derived from a transportation project that is not part of the same system or money derived from a different system, except to the extent that the surplus revenue of a transportation project or system has been pledged for that purpose;

(4) amounts received under a credit agreement relating to the transportation project for which the bonds are issued; and

(5) the proceeds of the sale of other bonds.

(b) Bonds issued under this chapter do not constitute a debt of this state or of a governmental entity, or a pledge of the faith and credit of this state or of a governmental entity. Each bond must contain on its face a statement to the effect that the state, the authority, or any governmental entity is not obligated to pay the bond or the interest on the bond from a source other than the amount pledged to pay the bond and the interest on the bond, and neither the faith and credit and taxing power of this state or of any governmental entity are pledged to the payment of the principal of or interest on the bond. This subsection does not apply to a governmental entity that has entered into an agreement under Section 370.303.

(c) An authority may not incur a financial obligation that cannot be paid from revenue derived from owning or operating the authority's transportation projects or from other revenue provided by law.