Indiana Code Title 9. Motor Vehicles § 9-21-8-44.5

Sec. 44.5. (a) As used in this section, “compression release engine brake” means a hydraulically operated device that converts a power producing diesel engine into a power absorbing retarding mechanism.

(b) A person who drives a motor vehicle equipped with compression release engine brakes on the Indiana toll road in a county having a population of more than one hundred seventy thousand (170,000) and less than one hundred seventy-four thousand (174,000) may not use the motor vehicle's compression release engine brakes instead of the service brake system, except in the case of failure of the service brake system.

(c) This subsection does not apply to a motor vehicle that has compression release engine brakes with a factory installed muffler or an equivalent after market muffler.  A person may not drive a motor vehicle equipped with compression release engine brakes unless the motor vehicle is equipped with a muffler in good working condition so that excessive noise is prevented.