There seem to be fairly regular (at least, more regular than one would like) AmTrak derailings in the US. That isn't to say I think it is AmTrak's doing specifically, I think it is like you said a maintenance issue coupled with everybody else who isn't on the train interacting with it.

Then there are the cases of engineers who are distracted and what not, but I'd imagine we're talking autonomous so that (hopefully) wouldn't be an issue.