let's distinguish between TRAFFIC stops and TERRY stops of a vehicle
in a traffic stop, in WA, only the person(s) suspected of committing a traffic infraction can be required to show id/identify themselves.
USUALLY, that's only the driver. if the passenger wasn't wearing a seatbelt or something, then the officer could demand he ID himself as well.
in WA state, if the car is stopped for traffic only, GENERALLY speaking, all other parties present not suspected of traffic infractions may also walk away. they cannot be detained.
obviously, don't jump from the car, but ask if you can leave if you want (if you are on a freeway, obviously, the rules are different but IN GENERAL, one is free to walk away if not a subject of the traffic stop)
if the car is being stopped pursuant to TERRY, then presumably the suspicion extends to all parties in the car and they can all be detained
parties are not required to show ID during a terry in WA state.
GENERALLY SPEAKING
case law has GENERALLY supported that officers can ASK for ID/a person to identify themself at a traffic stop if not a subject (passenger etc.) but must immediately return ID after writing stuff down so as to avoid constructive arrest, etc.
officers can detain on a traffic stop for a reasonable period of time. for example, it's been held up that even if an officer is finished with the citation (let's say 5 minutes) but is still waiting for warrant checks to come back via radio, that's fine. again, assuming radio doesn't take an unreasonable period of time.
