Punching the window and cutting the belt are the least of your problems. Maintaining your cool thought processes after the shock of that violent water entry is a major issue. Then you need to open and exit through the right door/window. In a situation where you're in a deep river, who's to say the car is upright? The car may roll on its side so you may need to follow the air and break the glass that's up. Maintain your up orientation, follow the air bubbles. Lots of stuff in the water.
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Better is the Enemy of Good Enough.
Okay, what’s your point??