🚗 Introduction
Under RCW 46.37.390, Washington law regulates muffler requirements, exhaust modifications, and vehicle smoke emissions. This statute ensures vehicles operate safely and minimize excessive noise or harmful air contaminants. Violations can result in traffic infractions, equipment citations, and potential fines.
What Does RCW 46.37.390 Require?
1. Mufflers Must Be in Good Working Order
Every motor vehicle must be equipped with a functioning muffler designed to prevent excessive or unusual noise. Use of devices like muffler cut-outs or bypasses is prohibited on public highways.
2. Emission and Smoke Standards
- Vehicles sold after January 1, 1971: May not emit smoke darker than Ringelmann No. 1 or emissions opaque enough to block an observer’s view for more than 10 seconds.
- Vehicles sold before January 1, 1971: May not emit smoke darker than Ringelmann No. 2 under the same 10-second limit.
Key terms defined in the statute:
- Opacity: The degree to which emissions obscure visibility.
- Ringelmann Chart: A U.S. Bureau of Mines standard to measure smoke darkness.
3. Exhaust Modification Restrictions
It is unlawful to modify a vehicle’s exhaust system to increase engine noise beyond factory specifications. Courts may dismiss infractions if there is evidence the vehicle was not actually operated in violation of this rule.
Exemptions:
- Vehicles 25 years or older
- Passenger vehicles used off-highway during sanctioned racing events
Penalties for Violations
Violations of RCW 46.37.390 are treated as traffic infractions. Penalties may include fines and mandatory repairs to bring the vehicle into compliance. Repeated violations may also attract increased enforcement scrutiny.
Practical Implications for Drivers
- Ensure mufflers are factory-compliant and in working order.
- Avoid after-market exhaust amplifications that increase noise levels.
- Keep vehicles properly maintained to prevent visible emissions or smoke.
If cited, drivers should review whether an exemption applies or if the citation was issued in error.
📝 Call to Action
Cited for violating RCW 46.37.390 muffler law or dealing with a noise/emission ticket? Contact Blanford Law at ken@blanfordlaw.com or 253‑720‑9304 for help understanding your rights and contesting citations.
