Boulder, CO Noise Ordinances: Vehicle Noise (2026)

Section 5-9-4 sets a flat decibel ceiling for any motor vehicle sitting or driving in the public right-of-way: 80 dBA on the A-weighted scale, rising to 88 dBA only for vehicles with a manufacturer's gross weight rating of 10,000 pounds or more, such as trucks and buses. 4-1974 sound level meter used for the general decibel table in § 5-9-3, at a distance of at least 25 feet from the vehicle. Section 5-9-8 separately bans car and truck stereo systems: no person may run an electronic amplifier in or attached to a motor vehicle if the sound is audible 25 feet away or produces vibrations that can be felt by someone outside the vehicle, at any hour of the day, including on residential streets.

That amplified-sound ban does not reach sound made on private property with the owner's permission that stays inside the property line. Chapter 7-3 layers on an equipment standard: § 7-3-4 requires every motor vehicle, moped, or low-powered scooter driven on a street to carry a muffler and exhaust system, in constant operation and properly maintained, that keeps noise at or below what the manufacturer originally installed; muffler cutouts and bypasses are barred outright, and a vehicle exceeding the Chapter 5-9 noise limits while on the street is independently a muffling violation. Both the owner and the driver can be charged under § 7-3-4.