Ack8236 Not true. Mythbusters did an episode on this.
If you wait until the car is fully submerged, the doors open fairly easily. You cannot open them when the car is partially submerged.
The recommendation was to wait for the car to submerge. As the water is rising and it nearly has filled the entire interior, take one last big breath, then wait for it to fill up completely.
At that point, you can open the door and swim to the surface.
People panic and waste a lot of energy trying to open the door earlier, when what they should be doing is trying to relax and take in deep breaths. Then, do as above, and your life is saved. Adam actually physically demonstrated it with a car in a pool, with rescue personnel on hand if needed. But he got out without incident.
Knowledge is power.
Having said all that, I suspect it is better to avoid driving into the water in the first place.