General Road and Highway Discussion

[BuildingScout]

But railways have occasional collisions, even with sophisticated signalling systems.

I don't know what gave you that impression. Most signals can be overriden by conductors. That is not a sophisticated system. In fact of the last three accidents I can think of off the top of my head all of them would have been prevented by a basic computer-over-conductor override.

Also keep in mind that the bar isn't zero accidents but less than 11 million accidents, which is the present number of car accidents in America per year.  The google car automated driving experience (3 million miles, a handful of accidents) suggest that present technology has already achieved met this bar.