How many fatalities are caused by cars traveling in excess of 90 mph? I don't know the number. I am sure it is greater than zero, but I would guess it isn't much larger than that (percentage wise) I'm not sure why you picked 90 mph. But I think any arbitrary number is going to have an issue. The speed isn't the issue. It is the difference in speed between the vehicles on the road at the same time as well as other factors. Consider than the fatality rate on the autobahn is about half of the rate as US.