The Legislature shall have no power or authority to in any manner lend the credit of the State or grant any public money to, or assume any indebtedness, present or future, bonded or otherwise, of any individual, person, firm, partnership, association, corporation, public corporation, public agency, or political subdivision of the State, or anyone else, which is now or hereafter authorized to construct, maintain or operate toll roads and turnpikes within this State except that the Legislature may authorize the Texas Department of Transportation to expend, grant, or loan money, from any source available, for the acquisition, construction, maintenance, or operation of turnpikes, toll roads, and toll bridges.