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

Thu Apr 5 02:28:22 UTC 2018

https://www.openstreetmap.org/changeset/57747093

shows the following for me, are you not seeing this?

Comment from Ds5rUy <https://www.openstreetmap.org/user/Ds5rUy>  2 days ago 

What's the rational for adding the no_u_turn restrictions for every single entry/exit to a roundabout where there are two physically separated ways?

We discussed exactly that in the #osm channel a few weeks ago, and IIRC came to the conclusion that this is not necessary or desirable.

There are no "no u-turn" signs at these locations, it's simply physically a really stupid idea to attempt a u-turn there.

Which is something that routing software should be able to derive from the geometry of the ways.

AFAIK, restriction relations are meant to represent signed legal restrictions only.

From: Clifford Snow <clifford at snowandsnow.us> 
Sent: Thursday, 5 April 2018 12:11
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?

I don't see any changeset comments in either of the two you referenced. I would suggest adding a changeset comment to get their attention.

You can also look on their github page to see what they are working on. https://github.com/Microsoft/Open-Maps/issues

Best,

Clifford

On Wed, Apr 4, 2018 at 5:23 PM, <osm.tagging at thorsten.engler.id.au <mailto:osm.tagging at thorsten.engler.id.au> > wrote:

Well, the edits seem to be made in JOSM, and the speed seems to be too low to be a bot. So I do think they are made by hand.

But this (and tens of other changesets are all titled "Added turn restrictions source: Probe”. I don’t know what “Probe” is, but I assume it’s some automated tool somebody wrote to find these supposedly “missing” turn restrictions. And now somebody is following the output of that tool to enter the turn restrictions into OSM.

Which really doesn’t make much sense to me, because of some tool is able to determine that this isn’t a good place to turn, then router software can do the same and doesn’t need explicit turn restrictions in OSM.

Especially given that (in my understanding) turn restrictions are meant to directly reflect a legal turn restriction that is signed “on the ground” with either signs or road markings, which these are not. 

Cheers,

Thorsten

From: Jo <winfixit at gmail.com <mailto:winfixit at gmail.com> > 
Sent: Thursday, 5 April 2018 09:53
To: Tag discussion, strategy and related tools <tagging at openstreetmap.org <mailto: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?

That is absurd behaviour. Seems like somebody programmed a bot.

Polyglot

2018-04-05 1:49 GMT+02:00 Tod Fitch <tod at fitchdesign.com <mailto:tod at fitchdesign.com> >:

Seems like tagging “noise” to me. I’d expect a router to use the roundabout itself because exiting, making a U turn and then re-entering the roundabout will be longer and thus slower. Since the no U turn relations are there to make routing work and a reasonable router won’t need them, I’d say they are “noise”. If I were to go in to fix something on that intersection, I’d probably remove the no U turn restriction(s). But I don’t think I’d go out of my way to find them.

Cheers!

On Apr 4, 2018, at 4:36 PM, osm.tagging at thorsten.engler.id.au <mailto:osm.tagging at thorsten.engler.id.au>  wrote:

I’ve noticed that someone from the Microsoft Open Map team is very busy adding turn restrictions all over the place (  <https://www.openstreetmap.org/user/shawat94/> https://www.openstreetmap.org/user/shawat94/ ).

In my local neighbourhood, I noticed that he added no_u_turn restrictions to all the nodes where a road into in/out of a roundabout is splitting (because of physical separation). Which basically amounts to 4 no_u_turn restrictions for every single roundabout.

e.g. here:

 <https://www.openstreetmap.org/changeset/57747093> https://www.openstreetmap.org/changeset/57747093

 <https://www.openstreetmap.org/changeset/57674063> https://www.openstreetmap.org/changeset/57674063

There is no actual no_u_turn sign in any of these locations, it’s just (mostly) physically a bad idea to attempt a u-turn here.

Just a few weeks ago I discussed exactly this in #osm and the conclusion was that it was neither necessary nor desirable to do this.

I made a comment about that to the first of the two changesets linked above, but haven’t gotten a reply.

So, what is the general opinion about this here? Should these turn restrictions be created or not?

Cheers,

Thorsten

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