Sadly accidents do happen.
Here is one guy's description of an accident in which his buddy died.
They were making a promotional film in which one had to go over a bridge and one under it.
WARNING. There is video of the crash but it is very quick and the resolution is quite low.
[youtubevideo]http://www.youtube.com/watch?v=ug1rCyeNujU[/youtubevideo]