I guess I am irrational as I have done it before. Not in a car, but on a bar stool.
Also, how big is the cop?
A bunch of details matter in suggesting how he would react. Also, I highly doubt the situation started out at 100mph. I would assume it started at something more normal then escalated. Grabbing someone and pulling them to you to get mean with them is something that wouldn't require a full fight/flight reaction as it usually takes place before that happens. All that said, I am not a cop, so throw out some of the thought behind this.