Here in Germany, the road classifications roughly match with the UK system, though the primary distinction is which government owns a road: A road owned by the federal republic (Bundesstraße), a road owned by a state (Landesstraße), a road owned by a county (Kreisstraße) and lastly, every other road (owned by municipality, place, landlord, etc.). The system roughly matches with highway=primary, highway=secondary, highway=tertiary and highway=unclassified/residential/service/etc to the importance of the road in relevance of Germany itself and the various regions (e.g. the federal state takes a particular interest of maintaining roads of national interest while the individual states particularly maintain these of statewide interest) (highway=trunk is a special case in which the distinction is strictly by structure i.e. grade separated and no overtaking allowed regardless who owns the road but this isn’t a universal practice and highway=motorway also have to be legally classified as this alongside being dual carriageways instead of just a single carriageway with no overtaking permitted).
That being said, there are plenty of exceptions for various reasons such as how the ownership of a better built bypass of a settlement may not have been transferred while the settlement’s main road is still part of a federal or state highway despite the fact that driving there through is impractical especially with a large vehicle like a lorry. Conversely, a lot of Kreisstraßen (but not Bundes- and Landesstraßen) lead to a dead end because they’re the main road to an otherwise isolated settlement and such highways would only have a classification as major as highway=unclassified in part because you can’t continue a highway=tertiary and also because such a road is strictly for local traffic only.
From my German POV, a highway=unclassified is any road under one (or more) definition:
- The highway leads to a dead end (at least for cars) but is exurban (few to no driveways). The road will be
highway=unclassifieduntil the next junction. - The settlement is minor and there aren’t any reason to take this road as a shortcut, regulations or otherwise (furthermore, such road will still be
highway=unclassifiedinside the settlement akin to the “no broken up classifications” of higher classification instead ofhighway=residential). - More rarely (and essentially an extension of the above), it can be used to tell that it’s the main trunk of the settlement’s traffic (essentially a very local highway) while the others lead to a dead end (making them
highway=residential).
In additon, highway=unclassified is also commonly used for local roads in an industrial area in Germany under the idea that such roads are non-residential because few people (if any) live there and the primary targets are the factories and businesses, though this isn’t a quite universal practice.[1]
Relevant discussion: Klassifizierung von Straßen in Industrie- und Gewerbegebieten - #11 by Mammi71 ↩︎