Tex. Transportation Code § 366.301

(a) To the extent permitted by the Texas Constitution, the department may agree with an authority to provide for or contribute to the payment of costs of financial or engineering and traffic feasibility studies and the design, financing, acquisition, construction, operation, or maintenance of a turnpike project or system on terms agreed on by the commission or department, as applicable, and the authority. The agreement may not be inconsistent with the rights of the bondholders or persons operating the turnpike project under a lease or other contract.

(b) The department may use its engineering and other personnel, including consulting engineers and traffic engineers, to conduct feasibility studies under Subsection (a).

(c) An obligation or expense incurred by the commission or department under this section is a part of the cost of the turnpike project for which the obligation or expense was incurred. The commission or department shall require money contributed by the commission or department under this section to be repaid. The commission or department may require the money to be repaid from tolls or other revenue of the turnpike project or system on which the money was spent. Money repaid as required by the commission or department shall be deposited to the credit of the fund from which the contribution was made. Money deposited as required by this section is exempt from the application of Section 403.095, Government Code.

(d) The commission or department may use federal money for any purpose described by this chapter.

(e) An action of an authority taken under this chapter must comply with the requirements of applicable federal law, including provisions relating to the role of metropolitan planning organizations under federal law and the approval of projects for conformity with the state implementation plan relating to air quality, the use of toll revenue, and the use of the right-of-way of and access to federal-aid highways. Notwithstanding an action of an authority taken under this chapter, the commission or the department may take any action that in its reasonable judgment is necessary to comply with any federal requirement to enable this state to receive federal-aid highway funds.