I also lived once in an apartment that was on a noisy street, I did all sorts of research on decibel limits in cities and briefly considered starting to record and trend using a decibel meter - then I remembered I have a day job.

At least in Seattle, there is an ordinance, but it isn't enforced often, and the most clear rules are some silly "if you can hear a sound system from 75 feet away from a car 'clearly'".

I reached out to the public non-emergency PR part of our police dept, essentially their summary was 2-fold, as I remember:

1. The most common noise enforcement calls were construction vehicles and semi trucks using jake brakes, both of which were a priority when there was opportunity to enforce (i.e. a pattern) 2. Many vehicles are very loud, whether legally authorized or not: sirens and emergency vehicles, Harley's, etc. Vehicle enforcement is rare. (They would not say never enforced, but that's the feeling I got)

In my opinion, the only thing louder than the motorcycles were all of the city buses. :(