[OSM-talk] Am I mapping this wrong, or should the router be fixed for this?

Maarten Deen mdeen at xs4all.nl
Mon Jul 27 17:18:11 UTC 2015

On 2015-07-27 17:58, James Mast wrote:
> I've been normally mapping slip lanes as '_link' highways at
> intersections since the beginning.  However, as most fellow US mappers
> know, they almost never have 'speed limits' posted for them, and that
> seems to help cause problems in some routing programs when they give
> those slip lanes a speed limit higher than the main highway.
> Anyways, I've been using OSMAnd recently for occasional offline
> routing on my tablet and have come across weird routing (I'd like to
> call them 'bugs') at some intersections that have 3+ traffic lights
> nodes at them because of the roads being divided.  Here, OSMAnd routes
> me onto a slip lane, makes a U-Turn on the side road, and then
> continues the across the main road to accomplish what a simple 'left
> turn' could have done [1], all to avoid '1' traffic light node.  So, I
> go report the 'bug' on the OSMAnd Google group [2], and then somebody
> forwards it to the GitHub site [3].
> In the response I get back on GitHub, one of the maintainers of OSMAnd
> says it's a 'map data' issue and closes it.  Claims that in the
> 'maneuver', since it avoids an extra traffic light node, it's the
> shortest route, even though it does that funky U-Turn.  Say what?!  I
> mean, honestly, if both MapQuest Open & OSMR can do that left turn
> 'normally' without needing to make a funky U-Turn, something has to be
> wrong in OSMAnd, right??  Sure, there isn't a 'NO U-Turn' sign posted
> for this maneuver, but still, the routing engine shouldn't be
> suggesting it since there isn't a 'NO Left Turn' relation there
> preventing the left turn from McKnight SB to Siebert EB.
> So, that leads me to my question.  Does anybody think I've tagged the
> intersection incorrectly?  This is how I've been tagging intersections
> like this from since the start, and I know most other US mappers have
> been doing the same.  Or should I start adding 'false' U-Turn
> restrictions to prevent the routing bugs and then be called out as
> 'tagging for the router', or even maybe start putting traffic light
> nodes at the stop lines for intersections that have both roads divided
> (and just leave simple one-node intersections as-is)?
> I'm very curious to see what others have to say about this to see how
> I'll move forward when I map in the future.  Also, don't hesitate to
> respond at the Google Group post or the GitHub one too as I get the
> e-mail notifications from them as well.
> -James
> [1] - (MapQuest routing, OSMAnd suggestion in [2] link) -
> https://www.openstreetmap.org/directions?engine=mapquest_car&route=40.53204%2C-80.01073%3B40.53002%2C-80.00614
> [1]
> [2] - https://groups.google.com/forum/#!topic/osmand/XJ-HVOHhKEM
> [3] - https://github.com/osmandapp/Osmand/issues/1501

It is a routing problem. No sane person would take that road and it 
should be possible to make an algorithm that does not take that road, 
even with the speed limit missing.
OSRM is flawed the same way in that it will blindly take a highway 
offramp and onramp because it is a few metres shorter, like in example 


I would not map it differently, I would like to urge router programmers 
to fix these issues in their router. I'm sure it's possible.


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