Comment by isaachier

I think you might be confusing "defensively" with perfectly. There are situations even defensive driving cannot prevent. For example, any car going 35 mph will need a few feet to brake if something jumps directly in front of it. Defensive driving just accounts for one's surroundings and likely outcomes. Seeing as the cars have been on the road in Arizona for a while, and this is the first we are hearing about a pedestrian collision, it seems the algorithm is pretty safe.