According to studies, over 10,000 water immersion auto accidents occur each year. Over 300 people on average, perish before getting out.
Wait until you are safely out of the water before attempting to call 911. Your escape from the vehicle is the most important thing to focus on initially. First, roll down the windows. If the electronic windows will not roll down, just wait while the vehicle fills with water. If the windows are still above the water line, go ahead and climb out. If water begins to come in as you roll the window down, try and remain calm as the interior fill with water. You have to allow the interior to fill in order to relieve the external pressure being applied by the surrounding water. Take a deep breath and as the car is nearly filled, try to open the door. Survival experts recommend leaving your seatbelt on until the last second, as water rushing in could disorient or possibly injure you. Also, this could give you extra leverage when attempting to force the door open. If for some reason you cannot open the door or window, try kicking out the windshield or breaking a side window as a last resort. A window punch will allow you to break glass without having to swing a tool or heavy object.
A factor that can change the dynamic of this scenario drastically is if you are not alone in the vehicle. If you have passengers with you, do what you can to keep them calm. If you have children with you, help the older children first so that they can help you with others or at least help themselves to safety. Having a plan in place is the best way to improve your chances of survival and those with you. Talk to your occupants and let them know what is happening and what needs to happen. If you travel with children regularly, talking to them about it before it happens can help.
The most important thing is to remain calm. Obviously this is much easier said than done. If you are struck by the airbag, you may be stunned. Also, it is hard to hold a breath when your heart is racing and carbon dioxide is building up in your system. Survival Systems USA, a firm that trains soldiers in emergency escape techniques, has found that it takes about 20 seconds to escape through the door of a submerged vehicle. A calm, relaxed person can hold their breath for 30-45 seconds under water, so if your heart is racing or you are panicked, you won't have much room for error.
Even the most buoyant vehicles will not stay above water for long. Float times include numerous variables, including unforeseen circumstances like how the vehicle entered the water and if there is damage. It also depends on how tight your vehicle is sealed prior to the incident. All things aside, a minute or two is probably all the time you will have to take the appropriate steps to ensure your escape and survival.