1) WPLG-TV did a live study of a driver's escape from a car that had plunged into a canal. The EMT present said to roll down the windows, allow the water to fill the car, then exit by door or window.
The "victim" (news-anchor Dwight Lauderdale) followed directions, but couldn't escape the sunken car!
He'd forgotten to unbuckle his seat belt and was hanging outside the window.
Recovering his senses, he pulled himself back inside, unbuckled, and swam to the surface.
2) Driving down to my [Florida] street, there's the correct right turn, but 50-feet sooner, is a boat ramp. Especially at night, it's an easy mistake to signal one's intention to turn down the boat ramp!
3) That a vehicle can roll
downslope under water shouldn't be surprising.