Indiana Code Title 8. Utilities and Transportation § 8-16-2-11

Sec. 11. If and when authority so to do shall be granted and conferred by appropriate legislation by the Congress of the United States, the department shall charge toll, in accordance with the provisions of this chapter, for the use of any bridge constructed under the provisions of this chapter;  and the department shall fix and establish the rates of toll to be paid for the use of such bridge, and for such purpose shall have authority to classify the users of such bridge into reasonable classes and to fix the rates of toll accordingly:  Provided, however, That such right to charge toll, and also said rates of toll and the classification of the users of such bridge so fixed and established, shall be subject to the approval and control of the proper authorities of the United States, as provided by the acts of congress providing for the supervision or regulation of the taking of tolls over interstate bridges.