I imagine frozen ground could cause such an injury, if hit with the right force, at the right angle. But, I don't know.
I know that a lot of newer vehicles turn on and off automatically when they to a stop, and I am really not sure how a key cycle is defined. I am inclined to assume that Trooper Paul's data somehow makes sense, but if it doesn't, then it just emphasizes perhaps that we really don't know enough about what happened, to reconstruct exactly what happened.
In theory, the initial impact at a low speed would not have propelled him backwards, but it would have been just enough to propel him forward onto the back of the SUV, to change his angle and maybe lift his feet off of the ground. He would have then been propelled backwards upon further acceleration.
You are right that I am saying this. I don't think I am working backwards. "Karen obviously hit him" is what the evidence, in its entirety, states to me. At least, the evidence clearly suggests to me that Karen's SUV was involved in some sort of accident which occurred at the same approximate time as and at the same approximate location where John suffered injuries that directly or indirectly caused his death. And I can't think of another reasonable explanation for what happened to John which would be plausible enough to establish reasonable doubt.