> What error in judgement did they make that makes them liable?
That's not the legal, or fair, standard. The results of my actions are the results, whether I made an error in judgement or just got unlucky. Of my action causes damage, I'm responsible for the results of my actions. Heck, even og my dog bites you, I'm responsible for the medical bill etc because it's my dog - you don't have to prove that I knowingly kept a dangerous dog or made some other error. (Unless perhaps you're trespassing, in which case maybe you caused the bite.)
> the passengers won't be making any operational decisions; there may not even BE passengers in lots of cases.
> They aren't operating them except to have called it up and set a destination.
If Amazon puts a log in the road, they are responsible for the results. If Amazon parks a regular truck in the middle of the road, they are responsible for the results. If they drive trucks with the new automatic emergency braking and their drivers completely rely on that to avoid accidents, they are responsible. Whatever Amazon puts on the road, they are responsible for the results of their actions in putting it there.
> If they crash, it is because the vehicle wasn't sufficiently able to cope with doing the thing it was made to do. Operating in traffic in the real world safely is their function. That includes windy days, or in traffic jams, or during a police road closure or construction detour.
Maybe such a thing will be sold some day. Right now, cruise control amd automatic braking aren't anywhere near what you've described. When that happens, of it ever does, Tesla will tell *UPS* "buy our self-driving trucks, you can pay fewer drivers." Tesla will show *UPS* under what conditions the trucks can be safely deployed (snow and ice?). UPS will make a decisiom for the purpose of saving themselves money, based on their discussions with Tesla. Note I'm not part of those discussions. I don't know of Tesla told UPS "these trucks can handle dry pavement autonomously. When there is ice on the road or other dangerous conditions you'll need drivers." As far as I know, Tesla may have told UPS "these trucks have driver assist to reduce driver fatigue."
If UPS's truck rear-ends me on an ice-covered road, I'm going to sue UPS. I don't know what Tesla told UPS about what conditions are safe and which are unsafe for the trucks. If UPS also sues Tesla for selling them bunk trucks, that's none of my business. That's all about the discussions and contract between UPS and Tesla.