...but, yeah, going 100 mph, clubbing a dude with the car, and that forcing the vehicle to a complete stop? Not bloody likely (unless said victim was standing in front of a concrete wall when he got hit or, possibly, if hitting the dude did enough damage to the vehicle to kill the engine).
Anyhoo, I'd simply ignore the 'complete stop' bit and perhaps replace with a damage check to the vehicle (forcing a stop
if, for example, crushing old dude with your Impala mashed the radiator back into the engine block and totally fragged all sorts of pulleys and flywheels/snapped belts, etc), factor in a loss of speed for the impact and/or damage, and then make a check to verify that the driver actually maintains control of the vehicle after said collision.
Yeah, I know; "Eol, that doesn't tell me a rassafrassin' thing!"
Like I said, not an 'official' or even 'house rules' answer, but something you might wanna take, tweak, and make fit into your own house rules.
P.S. Welcome to the Inn.