You are misunderstanding the situation. Anyone who was knocked unconscious will be unable to remember the moments leading up to being knocked unconscious.
Being rendered unconscious interferes with the brains ability to fix longer term memories. This is a routine occurrence for anyone who has been knocked out. Nobody can remember what happened just before they were knocked out. It's physiologically impossible.
So, for the time after the wreck AND leading up to it... he can't account for what happened?
If he reached and maintained the excessive speed for SEVERAL MINUTES (AND MANY MILES) leading up to the wreck... there is no way for him to account for THAT?
I had a car wreck and rolled my car over. I was not conscious for several minutes after the collision. But-I recall everything leading up to the wreck in VIVID detail. It's burned in my brain, it all was happening in slow mo....like a movie I'll never forget