You’re presenting a false dichotomy. There’s the third part which is “foreseen but challenging circumstances.” Also, “stopped car” can be VERY bad in many circumstances. Stopped on lane 2 of a motorway, stopped in running water, stopped in snow.

Also I suspect many “unforeseen” circumstances happen regularly. The unforeseen part is “what” and “when.”

... stopped on a railroad track.

https://www.independent.co.uk/news/world/americas/waymo-trai...