than think again. I was diving in this lake in PA where many different vehicles are sunk so divers can have fun. Most of them have operational parts such as doors, stering wheels, seats but no glass. I was practicing my skills and screwing around (those two go sometimes hand in hand) and tried entry into vehicles closing the door and trying to get out. It was hard. The water was preventing me from opening the door easily and that's with interior being flooded. I can only imagine how much harder would that be with a window rolled up and/or air space in the interior. Now add to it a fear/panic factor which casues you to use up air more and you are one step away from drowning. I also tried to make a dent in a sheet metal underwater simulating window breaking but again it would be so freaking hard due to water density. It would probably be easier to do it from the inside when there is still the air pocket left or using your legs which are much stronger if vehicle is flooded.

Just my 2 cents.