Best action to take if your car plunges into a lake?

The advice used to be to let the car fill with water and wait for the pressure inside and outside of the vehicle to equalise. However if you plunge into a deep river or lake then it could take a long time for the pressure to equalise, you have no air to breathe and you could be a long way under water in which case you'll probably die. The advice given now is to exit the vehicle as soon as possible either through an open door if this possible or through an open window.