[Tagging] Lane geometry in OSM

Marc Gemis marc.gemis at gmail.com
Thu Aug 2 19:21:33 UTC 2018

OSM has a free tagging model. That means that everybody can use any
tag they want.
But this is not workable of course. Therefore we try to seek consensus
on how we can tag certain features. One way to do this is by writing a
proposal, asking for comments, improving the proposal, and having a
vote on this.

But some people do not follow this workflow, sometimes they just use a
tag document it a bit and that's it. Others might pick up the idea and
start using the tag. This is "voting by using".

The server does no checking at all on the tags. If it did, that would
mean that there is a small group of people that decides what is wrong
and what is ok. That's against the spirit of the free tagging.

I think thet width:lanes:start/end was part of an "experiment" set up
by an experienced mapper. Unfortunately, he left the project before he
started the proposal phase of those tags.

If you like the tags, you can document them and ask for comments on
that proposal on this mailing list.

I don't know if I understand (4) correctly. example width:lanes=3|4|4
in case the left lane is smaller.
in case the road gets wider, you have to split the OSM way into 2, and
map the other part with width:lanes=4|4|4

The width:lanes:end/start are meant for those sections where a lane
ends or starts. It is not meant to be used on longer streches.

As for area:highway, it is my feeling that most mappers are still
working on more essential stuff (missing roads, addresses, POI) and do
not bother yet about the exact geometry of the road. With essential, I
mean objects that are needed for good routing, whether it is for cars,
cyclists, pedestrians or other categories of road users.
area:highway is needed for self driving cars, but we are not there
yet. For me, those features are just "experiments" by a small group of

Another tag you can use is
https://wiki.openstreetmap.org/wiki/Tag:placement%3Dtransition , it is
supported by the "lanes and road attributes" of JOSM.

You might be interested in the OSM Lane visualizer :



p.s. those questions were also asked on help:
(for those that do not follow that website)
On Thu, Aug 2, 2018 at 8:58 PM John Lambert <johnwlambert at gmail.com> wrote:
> Hello OSM Tagging,
> I have a question about the use of detailed lane geometry to OpenStreetMap, like (1) lane centerlines, or (2) lane boundaries, (3) variable lane width, or (4) lane connectivity.
> Currently, all I see are:
> (1) how many marked lanes are there on a highway, e.g. <tag k="lanes" v="4"/>
> (2) which lanes on a two way road are not distributed evenly between the driving directions <tag k="lanes:forward" v="3"/>, <tag k="lanes:backward" v="1"/>
> (3) the "turn=*" key, specifying the indicated direction in which a way or a lane will lead for turning or merging, e.g. <tag k="turn:lanes" v="reverse|through|through;right|right"/> <tag k="turn:lanes" v="left|left||||right"/>
> (4) uniform lane width
> width:lanes, width:lanes:forward, width:lanes:backward, maxwidth:lanes, width:lanes:both_ways
> It seems like we would need a "Way" to describe each lane's centerline. My understanding is that it is not permitted in OSM to add an extra "Way" tag to a specific lane tag currently. Is this correct?  I have heard from another user that the lane centerline model was the previous OSM model, but was scrapped and replaced with the current road centerline model.
> Also, another question I have -- would a line width have to be uniform across an entire "Way," or can different line widths be expressed for each separate chunk of the Way?
> I saw that there is a key that a few people have used: width:lanes:end and width:lanes:start. I did not see these in the OSM documentation. Are these just fields that people decided to add without approval? Shouldn't the OSM server reject such an upload?
> I saw that a proposed feature is street area (or similarly area:highway), where a Way would depict the polygon area of a street, but I'm interested in even more informative lane geometry than this. My understanding, is that this proposed feature will only allow the enumeration of drivable road areas, and not per-lane width/boundaries. There is a figure shown here.
> Thank you in advance for your time.
> Best wishes,
> John
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