[Tagging] Lane geometry in OSM

[Tom Hardy]

On Friday, 3 August 2018 09:49:07 CDT you wrote:
> On Friday, 3 August 2018 06:11:48 CDT Lionel Giard wrote:
> >  If you look at the wiki page about different lanes tagging (
> > 
> > https://wiki.openstreetmap.org/wiki/Lanes ), you can see that a suggested
> > way of tagging (in "Examples/Motorways") is using letter to indicate which
> > lane goes to where (when there is a transition). This could be used to
> > extent the width tagging for transition lane (where one lane split to two
> > (or conversely). There are already a lot of possibility to tag detailed
> > lanes, but we could indeed add the width in it !
> 
> [...]
> 
> I vaguely recall that, but I'll have to study to see what you're talking
> about, shortly.

So it appears the letter designations are stand-ins for the name or the ref or 
more specifically the name as it appears on signage.  It could be the name of 
a city for example.  I am having trouble relating it to width, but I think the 
width:lanes:start/end formulation could cover it.
> 
> Also, I often see a center lane for left turns in both directions, as in
> https://ecn.t0.tiles.virtualearth.net/tiles/a0213330110033323031.jpeg?g=6570
> That's next on my list.  It's currently tagged as a two lane road just a
> bit west of the intersection I referred to earlier.  Note the solid yellow
> lines which usually means "do not cross" to me, so I think I'll have to
> look up the law before I attempt to tag it.

My first take:

lanes=3
lanes:forward=2
lanes:backward=2
turn:lanes:forward=left|through
turn:lanes:backward=left|through

lanes:forward/backward might possibly be redundant.

I think of it as a suicide lane, and it might confuse JOSM's "Enhanced lane 
and road attributes" even more than it does me.  Well there is at least one 
way to find out.

-- 
Tom Hardy <rhardy702 at gmail.com>