The National Park Service did quite a few experiments on this and what they found is that panic is what kills people. THey donned scuba gear and rolled a car down a boat ramp into the water. Ran it over and over. In fresh water power lights and locks still work, so do headlights, etc... once there is water against the door, say more than half, you won't be able to open it until pressure equalizes. The end result, stay calm, remove your seatbelt (often forgotten), drop the window or wait unitl the pressure equalizes, escape. Oh, remember, if you use a punch/hammer/res-q-me on the window before the pressure equalizes you are going to get a facefull of high velocity water and broken glass.

Bill