Tex. Transp. Code § 284.034

A county acting through its commissioners court that issues bonds payable from revenues from tolls collected for the use of a project under this chapter and also payable from an unlimited tax authorized under Section 52, Article III, Texas Constitution, may authorize, under that section, and issue and sell its bonds and use the proceeds to call, redeem, and pay off its outstanding tax and revenue bonds under the terms of the bonds and make the project available for the free use of the public.