A:  I don't know, but not many. I can't speak for the small coasters at carnivals, or for some of the real old coasters, but at a major theme park like Disney, Six Flags, Paramount's King's Island, Cedar Point, etc., you are probably safer on a roller coaster than in your car, as long as you don't try to get out at the wrong time, or do something bad like that. (If you tried to get out of your car while it was going down the road, you'd get hurt too, right.)

  There is a ride safety information on the Internet somewhere. When you read the accounts of the accidents, you see that the problem is usually that the person did a really bad thing, like try to get out while the ride was moving.