Are police officers allowed to break traffic laws without their lights/siren on?

I constantly notice police officers failing to use their signals, rolling through stop signs, etc. when driving. Additionally, I was recently pulled over for speeding (got just a warning), but when the officer was talking to me, he said that at one point he was driving well over the speed limit in order to catch up... show more I constantly notice police officers failing to use their signals, rolling through stop signs, etc. when driving. Additionally, I was recently pulled over for speeding (got just a warning), but when the officer was talking to me, he said that at one point he was driving well over the speed limit in order to catch up to me. He didn't turn his lights on until he stopped behind me at a stoplight, and the light finally went green. I have always been under the impression that in order to break any traffic laws, police cars had to have their lights or siren on. I know that laws differ depending on region. I live in Portland, Oregon. Does anyone know the answer to this for sure?
Update: Just to clarify, I'm not trying to complain, and I'm not trying to fight what's going on. Just merely looking for some factual information on this topic. I'd rather get some actual backed-up information, rather than opinions about cops, etc.
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