I didn't say it would be easy, but it does get easier as the pressure equalises.

I've now searched around a bit, and it sounds like the best approach is to open the window. All the news reports I found in which the victim survived, they got out through the window, not the door. Apparently electric window openers usually work for some minutes after the car is submerged, and submerging itself will take several minutes - at least, if the doors are shut. There seem to be cases where the door was opened, causing the car to sink quicker, and the rush of water forced the door shut again, making things worse.

It's certainly best to get out as early as you can, and doors shut, window open seems to be the best way.