We ask that people stop spreading this misinformation that you can simply take one last breath as your car fills with water, the doors equalize in pressure, and then you open to escape. Myth Busters did 2 episodes to demonstrate this and would have died both times if they didn't have a safety backup diver. Don't chance you life on your single last breath of air. Roll down or break your windows early and escape as quickly as you can, but do so only after you've removed your seat belt.