Self driving on highways is already working. There are solutions for interacting with periastrians. Mercedes had a prototype where a virtual cross walk was displayed in front of the car to show it was waiting for the pedestrian.
#1 cause of pedestrian injury right there: car in lane 1 stops and {driver waves at pedestrians/car displays crosswalk}; pedestrians start walking; car in lane 2 doesn't stop.
A protocol incompatibility issue? Oh well, can't make an omelette without killing a few people :-/ In other words, this requires precise cooperation from multiple parties involved; one fancy car implementing this is insufficient.
