Taginfo shows that the tag has been used in just a few places (mostly one city in Poland) so it's not very well established, in spite of several thousand uses: https://taginfo.openstreetmap.org/keys/dual_carriageway#map
There are a couple similar tags that are a little less common: * https://taginfo.openstreetmap.org/tags/carriageway=dual (688 uses, the value =single is more common) * https://taginfo.openstreetmap.org/tags/type=dual_carriageway (1144 uses, mainly relations - so this appears to be a type of relation, perhaps meant to group together the 2 directions of a dual carriageway highway?) But fortunately the key name has a clear meaning in British English: a "dual carriageway" should be a road where the lanes in each direction are separated by a central reservation or barrier, aka a "divided highway" in American English. As pages like Key:highway and Tag:highway=trunk have long recommended, these sort of highways are usually mapped as 2 separate ways + oneway=yes. As we can see in taginfo (combinations), the key dual_carriageway=* is always used with highway=* and almost always with oneway=yes, so that works: https://taginfo.openstreetmap.org/keys/dual_carriageway#combinations Checking overpass-turbo shows that the tag is used on pairs of ways which are parallel, as expected. For example http://overpass-turbo.eu/s/QTv (try Poland for the biggest number) It also shows that most occurences of "dual_carriageway=no" are with highway=trunk (or rarely highway=motorway or highway=primary), and almost all "dual_carriageway=yes" are highway=primary, =secondary, =tertiary or =trunk. So, that's what I've based the page text on. I have not added mention of this tag to any other wiki pages or Map features. If people are interested in using it, I might make a proposal. But perhaps we will decided that database users should interpret the geometry and name=/ref= tags of parallel highway ways to add this information in post-processing. Does anyone know if that is feasible? On 2/20/20, marc marc <[email protected]> wrote: > Hello, > > Le 20.02.20 à 07:41, Joseph Eisenberg a écrit : >> I've created a page for Key:dual_carriageway based on existing usage >> in the database: >> https://wiki.openstreetmap.org/wiki/Key:dual_carriageway > > how did you proceed? is the tag added by only one contributor to whom > you asked the question to create the page based on his answer? > or did several contributors suing this tag answer consistently ? > > Because I noticed it with the depreciation of the undocumented tag > camp_site=camp_pitch : when a tag is undocumented, the real meaning of > the objects in the database depends on what was going through the heads > of the different contributors (for this particular tag, we have found 5 > meanings each used more than 100x and it took hours and numerous > messages to ). > > The great advantage of an undocumented tag is that we know that the > meaning is not documented. the contributors aiming at quality can > therefore avoid it. the users of the data too. > Conversely, a tag documented "by hidden guessing" degrades the quality : > Some people will believe that this is really the meaning of the objects > in the database when it's only a guess. at the very least, it would > require a big banner "a contributor guess that the meaning of the tag" > > Regards, > Marc > _______________________________________________ > Tagging mailing list > [email protected] > https://lists.openstreetmap.org/listinfo/tagging > _______________________________________________ Tagging mailing list [email protected] https://lists.openstreetmap.org/listinfo/tagging
