Let's talk about highway classification in OSM

[pavvv]

So I made a thread about the implementation of official classification tagging:

Official classification of highways

Hello, in order to allow for a more consistent usage of highway=*, I’d like to propose global tagging of the official, national highway classification. In some countries, highway=* already corresponds to the official classification, but that’s not the case everywhere. Now, ref=* usually already shows what the road is classified as but sometimes roads can have no ref and in that case, noref=* doesn’t give any information. Sometimes, at junctions, roads can have small sections of no ref but sti…

And if someone needs a reason for why importance is needed, I have an example.
Here is the the route between Warsaw and Prague when driving a passenger car: GraphHopper Maps | Route Planner

And here’s the same route for lorries: GraphHopper Maps | Route Planner

The first route would be tagged as importance=supernational and the second one as importance=national + importance:hgv=supernational.
There are countless examples like these which result from restrictions for lorries or better conditions for them on other roads. With the current tagging, a road will be treated the same for both passenger cars and lorries despite one being more important than the other. An importance=* tag solves the issue.