This is for Florida, but may be the same in other states. I have used Exemption B twice already to get out of loud exhaust tickets!
(6) EXEMPT VEHICLES.--The following are exempt from the operation of this act:
(a) Emergency vehicles operating as specified in s. 316.072(5)(a).
(b) Any motor vehicle engaged in a professional or amateur sanctioned, competitive sports event for which admission or entry fee is charged, or practice or time trials for such event.
(c) Any motor vehicle engaged in a manufacturer's engineering, design, or equipment test.
(d) Construction or agricultural equipment either on a job site or traveling on the highways.