ABC news has an interesting article on how you can increase your chances of survival when you find yourself inside a car slowly sinking under the water. The following is a summary.
Wear Seat Belts
"The people who got out without a scratch absolutely had their seat belts on," says Brian Brawdy, survival expert and a former New York City police officer. "If you’re knocked unconscious because you weren’t wearing your seat belt, you won’t be swimming to the surface."
Let Some Water Inside the Car
"You have to wait for some of the water to get in the car to equalize the pressure," says Brawdy. "You won’t be able to open the door, and as counterintuitive as it sounds, you’ve got to let some water come in."
"Wait until the water gets up to your sternum and that’s the time to take as deep a breath as you can," he says. "The water pressure would have started to balance itself out and you’re going to be able to swim out."
While waiting for your car to fill with water is certainly panic-inducing, experts say panicking could severely diminish your chances of survival. Staying calm and preserving your energy and breath for when you have to swim out will make a huge difference.
Many of those who fear suffocating in a sinking car are under false pretenses about what exactly happens when your car lands in water. The car actually takes longer to sink than we think.
While submerged underwater, the batteries will take a couple of minutes before it short out. In the meantime, the electric controls for the windows will still work.
When trying to break a window, use a sharp object. Using blunt objects including your fist and boots will not work.