Vehicle Mod Laws in Washington

Replacing the exhaust system is legal in Washington, but a muffler in good working order is required and cutouts or bypasses are prohibited. Modifications that make the exhaust louder than the originally installed muffler are specifically prohibited.

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Washington requires an adequate muffler and sets in-use 50-foot limits of 72–90 dBA; the oft-cited 95 dBA test applies only to pre-1986 vehicles.

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Smoked or tinted film on headlights and taillights is illegal in Washington. Headlights must emit white light and taillights must show red at the required visibility distance, and tint that dims or discolors them violates those requirements.

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Frames are the only permitted accessory, and only if they do not obscure license tabs or the identifying letters or numbers, with the plate plainly seen and read at all times.

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Washington requires front and rear bumpers at least 4.5 inches tall and caps their height at 22 inches on passenger vehicles, rising by weight class for trucks to 28 inches front and 30 inches rear.

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Washington requires no cover and permits two each of spot, auxiliary passing, auxiliary driving, and fog lamps, with a four-lamp cap on front lamps over 300 candlepower.

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Washington applies a rim-line test: no part of the vehicle other than the wheels may sit lower than the bottom of any wheel rim.

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Aftermarket neon/underglow is banned while in motion on Washington public roads; parked private-property use is allowed.

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Washington requires fenders, covers, flaps, or splash aprons adequate to minimize rear spray on every motor vehicle — and the device must be at least as wide as the tire behind which it is mounted, extending downward at least to the center of the axle.

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Greater light reduction is allowed along the top edge only if the product is transparent and does not encroach on the AS-1 portion or extend more than 6 inches from the top. Because the material must be transparent, a printed or opaque banner is not legal in Washington — only a clear tint band.

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Front side windows: minimum 24% VLT. Rear side and back windows: minimum 24% VLT. Darker limits apply behind the driver on some larger vehicles.

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