The actual standard
There is no decibel limit, but stock is the ceiling.RCW 46.37.537 bans modifying an exhaust so it is louder than the muffler originally installed on that motorcycle. Straight pipes also fail the separate cutout and bypass rule.
RCW 46.37.537 states that no person shall modify the exhaust system of a motorcycle in a manner which will amplify or increase the noise emitted by the engine above that emitted by the muffler originally installed on the vehicle, and that it is unlawful to operate a motorcycle that has been amplified as prohibited.
Read that carefully, because two things follow. First, the benchmark is your specific motorcycle as it left the factory, not some universal loudness threshold. Second, the statute reaches both the modification and the riding, so "I bought it this way" is not an answer.
Why the "95 decibel" number you heard is wrong
Riders trade decibel figures constantly, usually borrowed from another state or from an event rulebook. Washington does not use one for motorcycle exhaust. There is no number in the statute to measure you against and no number to hide behind.
The practical consequence is that this is an officer judgment call at the roadside, informed by whether the pipe is obviously aftermarket. A slip-on with the baffle removed is not a subtle modification.
The separate cutout and bypass rule
RCW 46.37.390 applies to every motor vehicle and bans using a muffler cutout, bypass, or similar device on a highway. It also requires the muffler to be in good working order and prevents excessive or unusual noise.
So straight pipes fail twice: once under the motorcycle-specific comparative test, and once under the general cutout and bypass prohibition.
Does "loud pipes save lives" hold up
It is the most repeated line in motorcycling and it deserves an honest answer rather than a slogan.
Exhaust noise projects backward. The vehicle most likely to hurt you is the one ahead of you turning left across your path, and that driver is in a sealed cabin with the stereo on, receiving very little of your sound. What actually buys you that driver's attention is lane position, a covered brake, and an escape path chosen before you need it. Those are trainable. Volume is not a substitute for any of them.
None of which is an argument against the pipe you like. It is an argument against relying on it.
One place it will stop you cold
Worth knowing if you plan to train or test on your own motorcycle: some ranges sit on shared or leased property with noise conditions attached. At our Silverdale range, personal motorcycles need a stock exhaust. Show up with straight pipes and you will not ride that day.
If you are unsure whether your bike qualifies, call before you book. It is a two-minute conversation that saves a wasted morning.