Texas Transportation Code - TRANSP § 457.103. Fares and Other Charges

(1) pay all the expenses necessary to operate and maintain the transit authority system;

(2) pay when due the principal of and interest on, and sinking fund and reserve fund payments agreed to be made with respect to, all bonds that are issued by the board and payable in whole or part from the revenue;  and

(3) fulfill the terms of any other agreement with the holders of bonds described by Subdivision (2) or with a person acting on behalf of the bondholders.