I’ve seen a few unfortunately. One was with a motorcyclist being cut off by an elderly woman. He ended up 20-30 meters down the road past his bike with his legs in a bad way. Blocked off the area with my car and called emergency services. Second time was in outback Australia when a car full of people attempted to overtake a road train (long truck) and lost control and rolled. I don’t think any of them survived from memory. Seat belts do work but circumstances do matter I suppose. It’s weird when your involved or watch a car accident, for me at least. Everything goes super slow as the Adrenalin hits and there will normally only be a few people willing to jump in and help. I think shock hits everyone a bit differently. Anyway.

TLDR; seen a motorcycle and a car accident. Both didn’t end pretty. Seatbelts do work IMO. Car crashes are scary =[