[Tagging] Feature Proposal - Voting - lanes General Extension

Tobias Knerr osm at tobias-knerr.de
Tue Mar 6 11:24:13 GMT 2012

Martin Vonwald wrote:
> 1) The objective part: How is it done currently? Take a look at my
> first example in the proposal - it's using maxspeed. How is maxspeed
> currently tagged? According to the wiki maxspeed:forward and
> maxspeed:backward should be used. What tells use taginfo? The
> forward/backward variant is used more than 7000 times, the right/left
> about 50 times. What are the access rules using? Forward/Backward.
> What is used: lanes:forward/backward or lanes:left/right? The first
> about 3400 times, the latter about 250. The first is also documented
> in the wiki.

You are mostly including legal restrictions in your analysis - and for 
these, forward/backward are an obvious choice, as no matter _where_ on 
the road you drive, a maxspeed:forward/backward affects you.

The much more relevant precedent are existing attempts to tag lanes. One 
example is indeed lanes:forward/backward. But there are other examples 
for existing lane tagging which are also documented on the wiki, and 
used more frequently than your example according to taginfo:

~ 11.500 cycleway:left/right
~ 10.000 footway=left/right, 22.000 if you count "both" (same proposal)
~  4.500 footway:left/right/both:*

> I also think that we should clearly separate those approaches:
> backward/forward for the directions of the ways/lanes and right/left
> for anything next to the ways. This would be consistent. At least in
> my opinion.

My suggestion for separating the approaches is:
* Physical placement of things relative to road centerline: left/right.
* Legal restrictions depending on driving direction: forward/backward.

But I have another question: Do you use :forward/:backward strictly as
* "forward" = right of the central divider/lane(s) if right-hand traffic
* "backward" = left of the central divider/lane(s) if right-hand traffic
* "forward" = left of the central divider/lane(s) if left-hand traffic
* "backward" = right of the central divider/lane(s) if left-hand traffic

Or would it be possible for hypothetical weird road layouts that the two 
are mixed somehow, i.e. that there is a "backward" lane between two 
"forward" lanes?

Because if you technically allow mixing of lanes, rather than enforcing 
a clear split between 2 parts of the road (or 2+1 with center lanes), 
renderers can't determine the lane arrangement *even if* they know about 
the local left-hand/right-hand rule.


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