thats a interesting way to enforce the law, that means that 90% of 50 state legal exhaust is not legal in Washington!!
I wish it was just a decible level from a certain amount of feet from vehicle, that would be an easy and defined way to determine if it is conforming to the law.
even that Washington does it leaves it up to a small amount of speculation, is it from when the car was new or after 15 years?? If it was just a set decible for al vehicles it would just be so simple!