Transformers... tanks, jets, cars, and trucks. Fair enough that is pretty standard right? They are hiding in plain sight in these disguises, hence the subtext "Robots in Disguise". So, lets just say... Jazz, is in a hurry, right? Guy is speeding down the suburbs, and gets pulled over... Does Jazz stop? If he does stop, is asked to show licence and registration... How does he give said licence and registration? Is he even registered? Hell, for that matter does he even have the hands to hand the information to the officer due to only having the ability to show a holigram of a human inside of him? Then again, to make it worse... I don't think any of the Autobots had any human drivers in them in the Movie-verse, possibly the only one even bothering to have a disguise in the movies being is Blackout. So, what would Jazz do? And, since when did my robots that are more than meets the eye, suddenly loose the art of their disguise?
Holoforms and holograms. If they're smart enough to make a realistic hologram that can interact they can make a realistic drivers liscence and registration and hack into the police systems so their records can be verified or they would simply out manuever the police.
Yeah, a bright white Porsche painted with red & blue stripes along with the number on the side is very discreet. Holograms work wonders.
Marvel did take a crack at trying to address the 'human' driver issue somewhat: But then if a police officer asks them to step out of the vehicle I suppose they're screwed.
