There is no requirement to identity yourself, but the police will regularly lock you up in jail until you do identify yourself. They can't _force_ you to identify youself, and you can't go to trial for not doing so (partially because they dont' know who you are, but even if they later find out for other means), but nevertheless police departments everywhere will lock you up until you provide ID if you are stopped for a traffic violation. There is a guy around here-abouts who will routinely gets stopped for speeding and refuses to show ID out of principal. They put him in jail. He's tried to sue them, and lost. If it made it all the way to the supreme court, I'm not sure what they would decide. But the point remains, in real life, they put you in jail. Just be aware of it.