Boulder County, CO Noise Ordinances: Vehicle Noise (2026)

070 requires every vehicle operating anywhere in unincorporated Boulder County to be equipped with a muffler in constant operation, and bars operating a vehicle whose muffler isn't properly maintained to prevent noise beyond what the manufacturer's original muffler produced. 080 goes further and separately bans operating any vehicle whose muffler has been 'equipped or modified with a cutoff, bypass, or any similar device or modification,' which is the section that reaches aftermarket exhaust cutouts and delete pipes regardless of the resulting decibel reading. These two sections work alongside the ordinance's numeric limits: Sec.

050(A) caps ordinary vehicles at 80 dB(A) on roads posted 35 mph or less (84 dB(A) above that), with different figures for older motorcycles and heavy trucks, while Sec. 050(B) holds any vehicle on private property or a non-road public property to a flat 78 dB(A). Measurement follows Sec. 040(A)-(B): 50 feet from the center of the travel lane for roadway sound, or 50 feet or more from the vehicle off-road, taken with an ANSI-standard A-weighted meter when wind is under 5 mph (25 mph with a screen).

Sec. 030 independently declares excessive vehicle sound unlawful regardless of the specific muffler condition. The definitions in Sec. 020(F)-(G) explain that 'muffler' means a device using chambers, baffle plates, or similar mechanical design to reduce exhaust noise, and 'motorcycle' excludes trail bikes, dirt bikes, minibikes, and go-carts not approved for public road use.