[Tagging] lanes=x vs. xxx:lanes=a|b|c

Martin Vonwald imagic.osm at gmail.com
Mon Dec 15 13:04:37 UTC 2014

Hi everyone,

As I received a lot of questions lately, I want to point something out
relating to the values of the lanes key and the number of lane-dependent
values within any xxx:lanes key.
* The number of lane-dependent values within any xxx:lanes key is equal to
the number of lanes on the road, no matter if those lanes are full- or
half-width and no matter what kind of traffic they are designated to. [1]
* The value of the lanes key is equal to the number of full-width(!)
traffic lanes which are available to motorised(!) traffic. There are even
more exceptions - please see [2].

Therefore the value of the lanes key must be equal to or less than(!) the
number of values in any xxx:lanes key.

  turn:lanes=through|through|right   <- three values
  bicycle:lanes=yes|designated|yes   <- three values
This example is correct as there are only two lanes available for motorised

I want to make clear that I'm not happy with the definition of the lanes
key. But the definition is this way for ages and I definitively will not
try to change it (current usage: 4.5 mio times).

Therefore I would like to ask everyone not to ask me to change the JOSM
style [3] to show an error in the above example or any similar situation.
It is very hard to interpret access conditions within a style, so I can not
interpret all of them within a simple drawing style and therefore the style
only shows an error if the value of lanes is larger than the number of
lane-dependent values.


P.S: If you want to change the definition of the lanes key and achieve
worldwide consensus, I will update the style within a minute.

[1] http://wiki.openstreetmap.org/wiki/Lanes
[2] http://wiki.openstreetmap.org/wiki/Key:lanes
[3] http://josm.openstreetmap.de/wiki/Styles/Lane_and_Road_Attributes
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