(a) Except as permitted by the ordinance authorizing the bonds or notes or the deed of trust or indenture securing the bonds or notes or as provided by Subsection (b), the revenue of a mass transportation system may not be used to pay any other debt, expense, or obligation of the municipality.
(b) An acquired mass transportation system may pay the municipality that acquired the system for the loss of ad valorem taxes previously paid by the owners of the system until the indebtedness secured by the taxes is paid.