I wouldn't assume a highway should be classified as different road types just because of different states of maintenance or surface quality.
Have a look into the OSM wiki at [how highways are classified in OSM][1].
Furthermore have a look at [surface][2], [smoothness][3] and [tracktype][4].
Tracktype is used not only in combination with highway=track.
highway=track. 4wd_only=yes exists, too.
Own experience: Two years ago I travelled a highway whose surface was partly new asphalt, partly crumbled asphalt, partly fine gravel, partly pebblestone.
All the way I tagged it highway=primary - since it was/is one. :)
Pictures:
[](http://malenki.ch/Touren/11/Galerie/Tag_21/slide_28.html)
[](http://malenki.ch/Touren/11/Galerie/Tag_21/slide_31.html)
[](http://malenki.ch/Touren/11/Galerie/Tag_22/slide_05.html)
[](http://malenki.ch/Touren/11/Galerie/Tag_22/slide_34.html)
[1]: http://wiki.openstreetmap.org/wiki/Highways#Classification
[2]: http://wiki.openstreetmap.org/wiki/Surface
[3]: http://wiki.openstreetmap.org/wiki/Proposed_features/smoothness
[4]: http://wiki.openstreetmap.org/wiki/Tracktype