Car under Water? Here's what you do

Car crashes into rivers and dams are common enough. So are floodwaters. Here's what you do if it all goes horribly wrong on the road and when you look out the window, all you see is water.

Crashes that involve submerging have a higher death rate than head-on collisions. You might think this will never happen to you, after all, we live in the driest continent on earth. The 28-year-old Queensland mother whose car plunged into the Mulgrave River yesterday with her 10-month-old baby on board probably thought so, too. Luckily she was able to escape with the baby because, luckily, the car was not fully submerged.

If the car had been fully submerged, water pressure on the outside makes it impossible to open the doors - at least until the interior of the car fills completely with water. This is a predicament because by then many people are hysterical, and at this point the best thing to be doing is waiting calmly...

Mythbusters in the US did a story on escaping from an underwater car wreck, following the floods that basically destroyed the Gulf of Mexico a couple of years ago. See it now:

how to survive a sinking car 

According to the military expert interviewed, here's the basic process (much of which is fairly counter-intuitive). 

1. Stay calm. Easy to say, but you've just been in a crash. You might be injured. The car might not be upright.
2. Take a quick mental inventory, a snapshot, of who is on board. Decide who needs the most help (in order if there is more than one passenger.
3. Get the windows down quickly and escape early if you can. The car might float near the surface for 30 seconds or more. If you can get a window down, escape through it early. You can break a window using a 'Lifehammer', which is specifically designed for the purpose, or by striking the window with something hard. It's also possible to break a window by kicking at it with your heels when lying horizontally across the car. Aim for the centre of the window. DO NOT try to break the windscreen, which is likely to be laminated and practically unbreakable. 
4. If the windows remain up you'll need to wait for the entire car to fill up with water and the pressure to equalise before you'll be able to shove the door open. If the car is sinking, this is your only option. Do not waste time and energy trying to force the door open against the pressure if there is a large air space inside the car. Don't open or break the window in this situation because you will be hit by a powerful jet of in-rushing water. Wait.
5. Remember to over-ride the central locking early - before the water stops the electrics from working. Make sure the doors are unlocked.
6. Remain in your seatbelt. Sounds dumb; it is, however a very good idea. Human bodies are buoyant. If you undo the seatbelt too early you'll float up and also lose the leverage you get from being anchored in the car. That leverage might come in very handy, for example, if you are required to free a young child from a baby capsule, or free an injured passenger.
7. When the pressure equalises and you can get the door open, take a big breath and hold it (there might be only a small air space near the roof at this point. Shove the door open, push/pull anyone who needs assistance out (once they're free you can let go of them; unlike in Hollywood, real people float). Swim for the surface. If you are disoriented and can't decide which way is 'up', follow the air bubbles.
8. If the door won't open, check the lock is at the 'open' position. Try other doors as well. If you have been in a crash it's entirely possible the damage from the impact might have jammed one of the doors. If necessary, exit via the window. Break the window as described above if necessary.
9. Keep your eyes closed until you emerge into the air. Petrochemicals in cars may have leaked into the water nearby. Some of these can permanently damage your eyesight.