Every vehicle in unincorporated Boulder County must have a working muffler with no cutoff or bypass. On roads, cars may not exceed 80-88 dB(A) depending on type and speed limit; on private property the cap is 78 dB(A).
Ordinance No. 92-28, Section 1.01.070 requires a muffler "in constant operation," and Section 1.01.080 bans any "cutoff, bypass, or any similar device or modification." On-road limits in Sec 1.01.050(A), measured 50 feet from the lane center, run from 80 dB(A) (most cars at 35 mph or less) up to 88 dB(A) (heavy vehicles over 35 mph); motorcycles get their own tiers. Sound from a vehicle on private property may not exceed 78 dB(A) (Sec 1.01.050(B)). Colorado's statewide muffler and vehicle-noise rules also apply.
Muffler and vehicle-noise violations are a Class 2 Petty Offense: $30 per violation, escalating $30 per repeat within a year to a $300 maximum, plus court costs.
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