Well, it's not car bombs we're talking about here. Assume you have a fleet of self driving cars on the road deployed throughout the nation. A vulnerability is

Well, it's not car bombs we're talking about here. Assume you have a fleet of self driving cars on the road deployed throughout the nation. A vulnerability is discovered that allows an attacker total control. They deploy that vulnerability, and cause every single car in the fleet to accelerate and aim for pedestrians. So the next bit we have to ask is: How many self driving cars would be on the road at the time this attack gets deployed. Multiply this with: How likely the driver/occupant will die in this event, how likely is this event going to kill or harm pedestrians, and how much structural damage would be done? Play with those figures for a bit. Personally, what I'd consider reasonable guesses at these numbers results in some very large bodycounts.