Imagine that you're driving in the San Joaquin valley in the winter, it's a clear night, that stars are visible because a recent storm washed all the crap in the air that floated down from the Bay Area. You're doing 70 or so, with scattered traffic, and a car in your lane about 10-15 car lengths ahead. Suddenly his lights disappear, and 1 second later your roll into a fog bank with 15-20 feet of visibility.

The driver ahead, followed your advice and slammed on his brakes. But because the fog is so thick, you can't see his brake lights, but that's ok right? You're already applying pressure to the brake pedal when you slam into the back of him. Then you're slammed into by the car behind you. Then a semi rolls in, and kills the lot of you.

It happens every freaking year.

I don't see that scenario happening with driveless cars, where each and every one of them are programmed to react to the same stimulus in the same fashion, and are perfectly aware of how the other cars would react.

I wonder if, with time, some kind of secondary radar system for cars will arise. If everyone was forced to have one in the car (as happens with planes), the mixing of driveless cars with regular ones would be greatly eased.

70 mph is clearly too fast in that situation. You're missing the point, however. The conversation was about how robocars will be safer than human drivers, because they're not stupid. It isn't a contradiction, to point out another scenario in which many human drivers are stupid.