Right, but humans are terrible at the happy path. I’d take 20% safer on the happy path over 40% less safe in unforeseen circumstances. The failure mode being “stopped car” is also not that bad.

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.”