> or, depending on who's doing the defining: every road a human could take a car on.

That's a distinction without a difference. Forest service and BLM roads are "roads" but can be completely impassable or 100% erased by nature (and I say this as a former Jeep Wrangler owner), they aren't always located where a map thinks they are, and sometimes absolutely nothing differentiates them from the surrounding nature -- for example, left turn into a desert dry wash can be a "road" and right not.

Actual "full" autonomous driving is crazy hard. Like, by definition you get into territory where some vehicles and some drivers just can't make it through, but it's still a road(/"environment"). And some people will live at the end of those roads.