Thornton, CO Noise Ordinances: Vehicle Noise (2026)

Section 38-441(a)(3)e makes it a violation to operate any motor vehicle, steam engine, stationary internal-combustion engine, air compressor, or motorboat without a muffler in good working order that is properly maintained and in violation of Table A's sound limits; no muffler or exhaust system may be modified with a cutoff, bypass, or similar device. Separately, subsection (c)(8) sets fixed drive-by noise ceilings regardless of muffler condition: 80 dB(A) for any motor vehicle (or towed combination) with a manufacturer's gross vehicle weight under 6,000 pounds, and 88 dB(A) for vehicles over that weight, except that neither limit applies on streets posted for speeds above 45 miles per hour.

Subsection (c)(9) separately bars sounding a horn or signal device except as a danger warning during an actual emergency, for only as long as the emergency lasts. Enforcement for vehicle noise runs on its own track: under § 38-452(f), a motor-vehicle noise violation is cause for an immediate summons and complaint (not a notice to abate), with minimum fines set by city council resolution, and § 38-452(g) allows a driver to get compliance certification if the violation is traced to faulty equipment that gets fixed and checked by a designated city compliance officer before the court date.