Yes that's ATVs. I've never flipped one, nor has any member of my family. Last year there was one girl in our group who was trying to do a hill that she was not experience enough to do and she flipped but it didn't land on her. There was also a guy that flipped - just being a guy and showing off....again the quad didn't land on him. We've never had anyone get really hurt and we sometimes have groups of about 25 people.
Here's a pic of a few of them: