Tex. Transportation Code § 228.254

(a) Under authority of Section 52, Article III, Texas Constitution, a local governmental entity other than a nonprofit corporation may, upon the required vote of the qualified voters, in addition to all other debts, issue bonds or enter into and make payments under agreements with the department, not to exceed 40 years in term, in any amount not to exceed one-fourth of the assessed valuation of real property within the local governmental entity, except that the total indebtedness of any municipality shall never exceed the limits imposed by other provisions of the constitution, and levy and collect taxes to pay the interest thereon and provide a sinking fund for the redemption thereof, for the purposes of construction, maintenance, and operation of toll projects or systems of the department, or in aid thereof.

(b) In addition to Subsection (a), a local governmental entity may, within any applicable constitutional limitations, agree with the department to issue bonds or enter into and make payments under an agreement to construct, maintain, or operate any portion of a toll project or system of the department.

(c) To make payments under an agreement under Subsection (b) or pay the interest on bonds issued under Subsection (b) and to provide a sinking fund for the bonds or the contract, a local governmental entity may:

(1) pledge revenue from any available source, including annual appropriations;

(2) levy and collect taxes; or

(3) provide for a combination of Subdivisions (1) and (2).

(d) The term of an agreement under this section may not exceed 40 years.

(e) Any election required to permit action under this subchapter must be held in conformance with Chapter 1251, Government Code, or other law applicable to the local governmental entity.