[Tagging] Lanes tag, way forward

Kytömaa Lauri lauri.kytomaa at aalto.fi
Fri Sep 23 16:00:50 BST 2011

>How does this sound for a compromise?
>Many ways are not tagged with the total number of lanes at all points,
>but only with the number of through lanes. Therefore, end users should
>treat the lanes tag as a minimum rather than an exact number. Subtags
>(lanes:straight, lanes:right, etc.) or [[Relations/Proposed/turn
>lanes|turn lane relations]] can be used to provide more detail as well
>as an assurance that all lanes are mapped.

The latter part of your compromise proposal dismisses all except one of 
the summary points, most notably the one that all previous guidelines call 
for splitting the way whenever the lane count changes, and tools that 
already consider the lanes tag as the total number (kothic, mkgmap, and 
other routing software). You don't provide any reasons why the heavy
arguments could be dismissed.

"Many ways have not yet been tagged with the total number of lanes at 
all points, but only with the number of through lanes of a longer section.
Therefore, data consumers can mostly treat the lanes tag as a minimum 
rather than an exact number."

So far in this thread only you and Mr. Murray have voiced the opinion 
that only "continuous through lanes" should be included. Even with the 24 
turnlanes plugin users, that's next to zero percent of all users. You did 
not answer why would the sometimes subjective "through lanes" count 
be more accurate than the "physical total". You are the only one who's
had the guts to mangle the tag documentation with the phrase
"There is no agreement on whether short turn lanes ..." 

Clarifying the documentation to emphasize the total number as the definition
from the beginning and in practice as the ultimate goal is not asking you to 
change your tagging habits, but to make sure others don't get the 
impression that it's ok to change the value to something else, if the total 
count is already tagged. 

As such, lanes:right/straight etc. would only work for oneway carriageways.
You'll need lanes:forward:right/lanes:backward:right etc. (Btw, unless there 
was some glitch in taginfo earlier today, there wasn't a single use of 
lanes:right/straight (and likely lanes:left) by then, now there's roughly 
160 total of both left and right. Also, the first other osm editor I mentioned
your idea to, thought that lanes:left is just "lanes on the left side of the way". 
Even with lanes:forward:right=* etc. you have to split at minimum at roughly 
every intersection, even in the simple cases, so splitting further is not an 
issue. And as others said, you'd introduce ambiguity when, say a two lane
oneway road ends at a T; lanes=0 lanes:left=1 lanes:right=1 - or if it's 
lanes=2, that's total of 4 lanes instead of the real two - unless the lanes=* 
is always the total number. Any system that would lead somebody to 
tagging lanes=0 seems just plain wrong.

>*Should someone tagging all lanes also tag at least lanes:straight
>(especially if changing from through lanes to all lanes)?

Could do. 

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