The recommended (and slightly terrifying) advice is to let the car fill first. Basically, use the time and air to prepare yourself. When the car fills, the pressure will equalise, and you can push the windscreen out with your feet.
Unfortunately, unless you’ve thought it through beforehand, most people panic.
ColeSloth@discuss.tchncs.de 8 months ago
Instead of pushing out, the water pressure will make it fold in on its own after you crack it.