I wonder if human nature might help make robot trucks safer on the road, by the magic of risk compensation (http://en.wikipedia.org/wiki/Risk_compensation). A robot truck will most certainly be marked distinctively so the human drivers know there's a computer at the wheel. Human drivers will perceive this robot truck as dangerous (at least I would, and I doubt I'm alone in that prejudice) and thus drive a little safer in its vicinity to compensate. Possibly, driving a robot truck down a street would even reduce the human-on-human accident rate.

And the robot truck companies would be insane not to protect themselves. They would be wise to take a page out of the commercial aircraft industry's playbook, and instrument the hell out of each vehicle. Continuous engine telemetry and redundant camera views of the immediate vicinity recorded on a 30-minute loop, frozen after a crash and a core dump of the "driver" appended to the record for crash reconstruction. It'll be a tough sell emotionally, that the robot truck was following the speed limit and stop lights, but we'll get there.