Texas Transportation Code - TRANSP § 365.041. Amount of Tolls

(1) pay all expenses necessary to maintain and operate the toll road project;

(2) make necessary payments and otherwise comply with any permit or franchise for maintenance or operation of the toll road project;

(3) pay the principal and redemption price of and interest on all bonds that the district is obligated to pay, regardless of whether the bonds were issued as revenue bonds;

(4) pay all sinking fund or reserve fund payments agreed to be made in connection with bonds or other obligations as they become due and payable to establish a reasonable depreciation and emergency fund;

(5) comply with any agreement made with the holders of the district's bonds or other obligations or with another person on the bondholder's behalf;  and

(6) recover a reasonable rate of return on invested capital.