How can I keep myself from flying through the windshield when I get in an accident?
Solution 1:
On PC, if you hold f, the character will buckle up, and won't fly out so easily.
Solution 2:
Well, simply you can't. It's real life physics that when you drive into a solid object with that much force that your body is sent flying. I tried using a roll cage to see if it helps you at all but to no avail.
There are rumors going about that if you wait in the car long enough without driving you put on a seat belt, I'll try to test this theory tomorrow and if it's true I'll edit this question.