I do think the "last 1%" may be a very hard problem to solve, but the majority of crashes are simply people not seeing things or making bad decisions. "Recognition Error" and "Decision Error" are the two most frequent categories of accidents which basically boil down to not seeing obstacles while performing a maneuver (changing lanes and not seeing a vehicle in that lane, turning and failing to see an oncoming vehicle) and driving too fast respectively. ( see https://crashstats.nhtsa.dot.gov/Api/Public/ViewPublication/...)

I don't see why the "last 1%" problem needs to be solved when we have hundreds of thousands of accidents every year caused by people not paying attention, not reacting in a timely fashion, and driving unsafely; all problems that computers are likely to excel at.