[Tagging] I can't support transit:lanes

Bryan Housel bhousel at gmail.com
Mon Jun 11 15:12:01 UTC 2018

> Two issues here.
> First, the tag is not “transit:lanes” the tag is “transit” and it can be used with the generalized “:lanes” suffix. 
> There are general rules for the :lanes suffix which can be added to pretty much any tag you would have on a highway were the value could be different for different lanes. See https://wiki.openstreetmap.org/wiki/Lanes <https://wiki.openstreetmap.org/wiki/Lanes>
> It’s the same with e.g. “turn:lanes” (a “turn” key with the “:lanes” suffix) or “access:lanes” (a “access” key with the “:lanes” suffix).

.. none of this matters because the tag can’t go on a way anyhow.

> Second, the “transition” tag is already in use: https://taginfo.openstreetmap.org/keys/transition <https://taginfo.openstreetmap.org/keys/transition>
> Now, as far as I can tell, these are pretty much all transition=yes tags on power=tower or power=pole nodes. These seem to be left-overs from a previous tagging scheme, which has been replaced by the use of the location:transition=yes tag (and at 342 vs 13388 uses that seems to have been well accepted by now). 
> So I guess it might be possible to coordinated with people that are involved in power mapping to have these remaining ones retagged to free up the transition key.
> The type=transition value is currently unused, so in that regard the change would be fine.

Ok, so add a new type of relation and call it `type=lane_transition`
https://wiki.openstreetmap.org/wiki/Types_of_relation <https://wiki.openstreetmap.org/wiki/Types_of_relation>

> I agree that this tag when used on ways is problematic from an editor perspective. 
> Though by following pretty simple rules, the editor could prevent the transit(ion):lanes tag on a way from breaking:

Maybe seems simple to you, but I’m not going to do it, and the JOSM and Vespucci folks have also already said no too. 

> Transit relations have no via, and they don’t need a via. The from and to way should always touch at exactly one node. Otherwise they are invalid. So you can always determine the “implicit” via node from that.

I’ve already written plenty of code to deal with turn restrictions.  There are lots of rules for splitting and joining things to other things depending on where the via node is. 

If you are curious, here is a recent commit where I tried to improve iD’s handling of this.
https://github.com/openstreetmap/iD/commit/87841fc4035c7de9e0f58ca50f05f65723ad5226 <https://github.com/openstreetmap/iD/commit/87841fc4035c7de9e0f58ca50f05f65723ad5226>

In other words if this new relation works like a turn restriction, it’s already mostly supported… Otherwise expect basic editing (like splits, joins, connections) to break it.

Thanks, Bryan

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