A couple years back there was an article about being able to keep an "autonomous" vehicle from moving, by simply making a large circle around it on the ground with paint or something white. The issue with so-called "AI" systems right now, whether in vehicles or anything else is a decided lack of "common sense."
The common sense to be able to realize that the line in front of the vehicle is NOT a lane marker and just drive over it, the common sense to realize the sudden surge of CPU utilization doesn't warrant an alert being sent out because it happens EVERY week at the same time, etc.
Granted, of course, not every human has the same level of common sense, but most do.
Honestly, I'm with David.Poole, I'm mostly OK with autonomous trains, I'd even be OK with autonomous vehicles in a "convoy" sort of situation, where at a minimum the lead vehicle is being actively driven by a human and the remainder are just "following the leader," yet even then I'd want a persons' butt in the seat in case a sensor glitches or other such unforeseeable events.