I propose to add File:Forest road damaged by truck traffic.jpg - OpenStreetMap Wiki
to
very_horrible dirt and earth
current image at Key:smoothness/Gallery - OpenStreetMap Wiki is rather mud, not dirt and earth
idea is from User:Rhhsmits/SmoothnessGallery - OpenStreetMap Wiki (note, other changes proposed there were discussed in Revision of Smoothness Gallery ) - here I am proposing to apply solely this one
BTW, this looks passable by "heavy-duty off road vehicles " to me but also very_horrible at Key:smoothness - OpenStreetMap Wiki looks passable by them to me