One major key to self-driving cars is that all cars be connected together through a common network. They then communicate their position and speed. For example, take two cars approaching an intersection at the same speed so that they are on a collision course. In today's system, a traffic light would be green or red for one and the opposite for the other. One car would have to stop and let the other car through the intersection. With SD cars (or a smart traffic system) one car would speed up a little and one would slow down a little. They pass through the intersection within seconds of each other but safely. Nobody has to stop. Now imagine if you had hundreds of cars doing this...all zooming in/out of the intersection within seconds of each other. Nobody would have to stop. That would be amazing. In order for this to work they would have to be all linked up to each other. One single car not linked up would mess up the system. Traffic lights would then need a 4th signal-Automatic. The G/Y/R would be for back-up only for an outage. It will start on toll roads (sign would read SELF DRIVING (SD) only Traffic). Then it would spread. It would take awhile for all roads to adapt. We would all lament not being able to drive ourselves sometimes but most of the time I suspect it would make our lives much easier. There would still be plenty of places to go "manual"....
Looking forward to it.