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

37, Vehicle Lighting and Other Equipment, sets the county's muffler and vehicle-noise standards. 205(A) requires every motor vehicle to be equipped at all times with a muffler in good working order and in constant operation to prevent excessive or unusual noise and annoying smoke, and it specifically bans muffler cut-outs, bypass pipes, or similar devices on any vehicle driven on a county highway. Subsection (B) adds a parallel smoke standard: the engine and power mechanism of every vehicle must be equipped and adjusted to prevent the escape of excessive fumes or smoke.

Both rules trace to Ordinance 3748, adopted in 1968, and remain in force unchanged. 37 (the state vehicle equipment code, which covers mufflers) is a misdemeanor. The chapter separately targets engine/compression brake noise. 197 declares compression-brake use in residential areas a public nuisance and bans it outright on 26 named roads and highway segments countywide, from Old Highway 99 SE/SW and Marvin Road SE (SR 510) to the northbound lanes of I-5 between Exit 111 and the Pierce County line. 197(E), unless an emergency situation makes the brake necessary to protect persons or property.

Neither section carves out an exception for aftermarket exhaust systems marketed as off-road only: if the vehicle is driven on a county highway, the muffler standard applies regardless of intended use.