Some benefits of self-driving cars only come in when they hit certain market-shares. For highway driving there are big gains when you have enough for a dedicate

Some benefits of self-driving cars only come in when they hit certain market-shares. For highway driving there are big gains when you have enough for a dedicated lane, and when cars can "draft" one another, but the biggest gain will be in cities when (if) we get to 100%. At that point we can do away with all traffic lights except for pedestrian crossings. Not only will stop signs be unnecessary, cars could approach intersections at speed, knowing that there was a gap in the cross-traffic for them to fit through. If you let a single human-driven car onto those streets you couldn't implement anything like that, though.