Not sure if its still available and I am not home to get the authors but there is a book called Motorsport Medicine that was published back in the early 90's. Very interesting book with charts and graphs regarding impacts
and g forces.

If the time trial driver broke the same bone as Earnhardt and others not a lot of movement is needed. Its sudden acceleration and deacceleration of your head and neck over a couple inches maybe a little more as the harness stretches that causes the injury. If I remember correctly the bone is small and between the ear and neck. A Hans device can help.

I haven't looked at the book in years. No need I have low speed sheep beating me up.

Dave Apker and the collies