[Tagging] Dispute prevention: meaning of lanes tag

Andrew Errington erringtona at gmail.com
Mon Apr 30 10:30:40 BST 2012


On Mon, 30 Apr 2012 00:29:52 Kytömaa Lauri wrote:
> >Before that I added a point in the Open issues section about lanes=1.5
> >and modified the note at the end of the section Narrow road. As
>
> So, today I got a chance to revisit an unpaved residential road
> I've tagged as lanes=1.5 in the distant past. Here's two
> pictures of it (in one)
>
> Above, usual traffic drives almost in the center of the road,
> as if it were lanes=1.
>
> Below, the car in picture has it's right side mirror almost
> touching the fence, and there's 2.2 meters of the
> carriageway free for oncoming traffic, 2.6-2.7 meters
> of space to the fence on the other side of the road.
> Oncoming cars can get past each other, so it's not
> lanes=1. Yet all driveers will slow to a crawl, or at least
> to a jogging speed, so IMO it can't be lanes=2,
> either.
>
> http://i46.tinypic.com/2cfqivn.png
>
> Which value would people use for the lanes=*?

Sometimes the answer is "It doesn't matter."

If you tagged it with lanes=1, but not oneway=yes, then it's clearly a 
bottleneck and should be avoided by routers.

If you didn't tag lanes=* at all and you didn't have oneway=yes then my 
assumption would be lanes=2 (because it's not one way).  Or you could tag it 
explicitly with lanes=2. Either way, map users would probably complain that 
it's too narrow for certain types of vehicle, so it should be re-tagged 
lanes=1.

If you tagged the width then it wouldn't matter if it was lanes=1 or lanes=2 
because we can see the overall width and use heuristics to decide if it's a 
slow road or 'normal' road.

Furthermore, if it's classified as highway=residential that would be a hint 
that it's a narrow road not to be driven too fast.

Any of these factors, either assumed, or explicit, should be used by a route 
planner to make this road unattractive for routing.

It's very tempting to add explicit values for every tag, but I really think 
sometimes it just doesn't matter, and we can get the same meaning for 
combinations of other tags (even if the tags are absent).

Best wishes,

Andrew



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