Mason County, WA Noise Ordinances: Vehicle Noise (2026)

Section 9.36.130 sets in-use motor vehicle noise performance standards for unincorporated Mason County. Subsection (a) caps sound levels measured at fifty feet from the travel lane, with Table 1 setting motorcycles at 78 dBA at or under 45 mph and 82 dBA above it, light vehicles under 10,000 pounds GVWR at 72 dBA under 35 mph and 78 dBA above it, and heavier vehicles over 10,000 pounds GVWR at 86 to 90 dBA depending on speed. Subsection (b) requires every motor vehicle on the public highways to carry an exhaust system and muffler in good working order at all times, and subsection (c) separately bars tire squeal from rapid acceleration or excessive cornering speed, exempting only emergency braking. Subsection (d) adds exhaust-outlet limits measured at twenty inches, capping motorcycles at 99 dBA and lighter vehicles at 95 dBA. Enforcement runs through Section 9.36.150: violations are traffic infractions handled under RCW Chapter 46.37, officers need training in sound measurement before citing a vehicle, and a seller or manufacturer offering a noncompliant new vehicle for sale faces a civil penalty of up to $100 per vehicle.

Layered on top, Chapter 10.34 separately targets unmuffled engine compression brakes, the loud 'jake brake' sound from heavy trucks. Section 10.34.010 prohibits their use countywide except when necessary to protect persons or property and the situation cannot be avoided with alternative braking, and the county engineer posts warning signs under Section 10.34.020 for vehicles of 10,000 pounds or more, whether or not signs are posted. Section 10.34.030 sets escalating traffic-infraction fines of $250 for a first violation, $500 for a second, and $750 for each violation after that, enforced under RCW Chapters 46.63 and 46.64, waived only for a genuine emergency.