From the OpenStreetMap wiki:

In a rural context, unclassified roads might be distinguished from tertiary roads in the same geographical region by their:

Being narrower, such that vehicles might even need to slow down to pass in opposite directions;
Being unpaved, in less populous or poorer regions when the tertiary roads are not;
Being used more for access than for through traffic between towns and villages;
Lack of any visible classification; or,
Lower classifications, for countries which classify both and where the official classifications drive OSM tagging.

That IMO describes this road. I could add some additional tags like  surface=*, width=*, lanes=* and smoothness=* 
