[Tagging] Feature Proposal - RFC - junction=intersection

Matthew Woehlke mwoehlke.floss at gmail.com
Fri Jul 10 18:13:55 UTC 2020

For illustrative purposes, I went ahead and tagged 
https://www.openstreetmap.org/way/175473372. (I chose this intersection 
because the way was already split, so the only edit needed was to add 
the tag.)

On 10/07/2020 10.15, Matthew Woehlke wrote:
> As some of you may recall, I'm working on a project to do traffic 
> simulation with the help of OSM data and SUMO¹.
> One of the issues that SUMO has is that the typical method of modeling 
> intersections (which I don't propose to change, mostly) results in SUMO 
> thinking there are multiple intersections where there should only be 
> one. For example, intersections of two dual carriageways produces four 
> intersections and makes the turns much sharper than in reality.
> My use case isn't the only one that has issues with this sort of thing; 
> routers can "see" more traffic lights than actually exist and can (so I 
> hear, anyway) give directions that are potentially confusing. 
> Intersection modeling is a long-standing issue that has had multiple 
> previous proposals.
> The major two prior proposals of which I'm aware are to map the 
> 'footprint' of the intersection as an area, or to create relations to 
> map the intersection. Both are difficult, both to model, and for tools 
> to parse. The area proposal has potential rendering issues.
> I am proposing² a *much* simpler alternative, which is to simply tag the 
> portions of a road that are "part of" an intersection (i.e. the 'm', 
> 'n', 'p', 'q' segments of 
> https://wiki.openstreetmap.org/wiki/File:Doublejunction.svg) with 
> junction=intersection. This is straight-forward to model, and I believe 
> solves most of the issues for a majority of affected intersections. 
> (Exceptions likely exist, but 'perfect' is the enemy of 'good', and 
> right now we're at 'bad'.)
> Comments would be appreciated!
> Also, should I start just doing this for the areas I'm trying to use for 
> my project, or is it better to wait for some degree of consensus?

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