[Tagging] no_u_turn restrictions for every entry/exit into a roundabout when the way is split because of physical separation?

osm.tagging at thorsten.engler.id.au osm.tagging at thorsten.engler.id.au
Fri Apr 6 00:45:54 UTC 2018

I never said anything about _not_ having some way to encode such default rules. In fact, if you look at my recent posts here, you will see that I specifically pointed out the current lack of such a schema as an issue that needs to be solved. I also pointed out that the lack of “permission” relations is another issue that needs to be solved. I’m directly affected by both of these as I’m in Queensland and “no u-turn at signal controlled intersections” is the law in queensland.


In regards to the wiki, while it may not be “gospel”, there are usually reasons for the statements there, especially with things that have been unchallenged for a long time and which had been discussed in detail before (you did bother to look at the iD issue I linked, right?) So as long as it isn’t case of recent drive-by-night wiki fiddling, some thought should be put into figuring out why that statement is in the wiki instead of simply disregarding everything.





From: Paul Johnson <baloo at ursamundi.org> 
Sent: Friday, 6 April 2018 10:12
To: Tag discussion, strategy and related tools <tagging at openstreetmap.org>
Subject: Re: [Tagging] no_u_turn restrictions for every entry/exit into a roundabout when the way is split because of physical separation?


On Thu, Apr 5, 2018 at 5:06 PM, <osm.tagging at thorsten.engler.id.au <mailto:osm.tagging at thorsten.engler.id.au> > wrote:

I tought it was obvious, but let me spell it out: such restrictions represent a default which we should be recorded somewhere (not necessary inside OSM) once and observed by data consumers, not by creating potentially 100000’s of relations to again and again encode the default behaviour.


Why not have a schema, in the data, for encoding this?  Maybe a relation with the outermost administrative area to which it applies...







This is exactly the problem that exists in Brazil, where u-turns back onto the same way at intersections are generally prohibited without any explicit sign allowing them, so some mappers add 4 no_u_turn at every single intersection node.


Please refer to: https://github.com/openstreetmap/iD/issues/2527


In fact, it is also reapet, IN BOLD, on the main relation:restriction page: https://wiki.openstreetmap.org/wiki/Relation:restriction


*         Don't map turn restrictions that are the default for a given jurisdiction and are not signed. It is much better to ensure that routing engines embody the regional rule rather than mapping every occurrence as a turn restriction. This applies particularly to unsigned U-turns in Brazil, where using turn restrictions will require hundreds or thousands of restrictions and micro-segmentation of all roads which in turn make editing data hard.


Again, this falls back on the whole "quoting the wiki as gospel" part that I initially beefed about. 

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