Robert argued here that country-specific restrictions should be always expressed by tags so that routers don't need to know those specific rules/laws. He gave the maxspeed tags as an example, which we explicitly tag even if they are based on implicit laws.
I think this generalization is goes too far. For the access tags (and we do discuss access tags here), it is common practice to have country-specific defaults on certain highway types as listed in the wiki [1] and only tag what contradicts those defaults. I don't see why it would be needed to switch that to explicitly tagged values. Opposed to maxspeed, we are talking a large set of different tags here where both tagging as well as legislation is in constant change. Based on these asumptions, I would argue that it would be enough to specify if a compulsory exist or not and leave the details of which type of vehicle can under which conditions use the road or not to the router, which should implement those based on national defaults. So at least the legislation changes can be implemented at a central point. (This is already the default, so no additional change needed for that.) I would prefer an additional tag over a replacement for bicycle=no, as this would allow an easier migration due to not breaking older routers. (This is why I would vote 'no' on the proposal.) I would also say that stating that there IS a compulsory cycleway is a first step, but not enough. To check for certain conditions (width, direction, reachable destination, obstacles, surface), the router would need to know WHICH way is the compulsory cycleway. We can either do this with a relation combining the highway and the cycleway(s) or with tags and self-created references. I would clearly prefer the first. I think neither storing all the information needed for those decissions in the highway tags (instead of the cycleway tags) would be a doable workaround nor pre-interpreting them by the mapper and tagging the result on the highway. As stated above, those interpretations would be based not only on (ever changing) local administration but also on very subjective opinions. As a user, I'd rather have those opinions baked into the routers I can chose, not in the map data all routers have to use. My 2 cents, Chaos [1] https://wiki.openstreetmap.org/wiki/OSM_tags_for_routing/Access-Restrictions#Germany
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