By a ratio of 3:1 fatal accidents occur more on rural roads, where speeds are higher, roads are narrower, more twisty and hilly, road surfaces not so good and often covered in leaves or mud - this is the area where autonomous cars could make the most difference ( if they could ever travel above 15mph ), but it is the area where they will be least at home. With hedges and trees scattering back random reflections to sensors, road markings missing or obscured by leaves or mud and roads not cleared of snow. Initially ( and IMHO for a long time ) AV will be restricted to small and well defined city areas, where accidents are normally a lot less serious than in rural areas. Will it be possible for AV to pass on a single track road with passing refuges like normal human controlled cars do all the time ? How about if an AV has to cross a double white line to pass a slow or stopped tractor or vehicle, and how about detecting and safely passing cyclists ? Just a few on many scenarios that humans take in their stride and hardly need to think about.