For them to have a fully loaded semi on the freeway and the driver to get in the back seat was blatantly irresponsible. This experiment should never even have been legal.
According to TFA, they've been preparing for this one run for 6 months. Mapping it out, training the AI on the dynamics of loaded trailers, sending humans down the road to see when the safest time is, etc. You can bet more than a few lawyers were consulted during the course of this work between two companies.
AI cars have such a low safety requirement, they're going to have to swerve around them to avoid tripping over it. In cars, they have soccer moms with screaming kids and middle managers gabbing on cell phones, distracted driving accounts for half of the traffic out there. In the case of a commercial trucker, we're talking overtired and bored. An AI with an adequate vision system can easily out perform the most distracted drivers on controlled roads in perfect weather. We talk about self driving cars as though they only win the safety game with 0% accidents, but if safety concerned moms and wealthy business people buy them, I think tail end of the safety curve is going to get chopped off, bringing the averages up. Hell, I'd chip in for a retrofit on a BMW I keep seeing on my commute.