I've had a look for uk guidance as the uk's ordnance survey was
mentioned, and a lot of older uk advice appears based around a now
historic view that 'cars = saloon cars' and were 1.8m or less. If cars
were assumed to be 1.8m wide then implied OS figure of 4m for two lanes
makes sense.
I am not sure we should base the lanes tag value on typical car width.
IMO the lanes tag should *not* be another kind of estimate for the width.
A further problem is the definition: For example the "euro track" has a
maximum allowed width of 2.55m without mirrors (refrigerated ones even
2.60m). This would be as fair as basis as a "average" car in UK or a UK
guide. And in US or India we may find another situation again.
My opinion:
If the width of the road can be estimated and no lanes are marked: We
should tag the width (of the carriageway(*)) only (or est_width or
width+source:width) and no lanes tag.
(*) Sadly the width itself is pretty ambiguous tag at the moment (e.g.
is it the width of the complete street or just the carriageway, etc.).
But this is a topic for its own.
When you look at following example:
http://wiki.openstreetmap.org/wiki/File:Bangalore_India_traffic.jpg
then I conclude: If there are no marked lanes, it lanes gets simply too
subjective.
My current practice:
On non-residential areas (tertiary, etc.) I typically tag lanes=2 only
if the road allows *two* trucks (that don't require police escort
because they are wider than allowed, means >2.6m) to pass. In my area
this means >5.2m.
In residential areas/streets I omit lanes if they are not marked.
Parking allowance and parking cars on the street/carriageway make the
situation very complicated. Look here:
http://bit.ly/I2hna7
While the carriageway in this example is more than 6m wide and allows
two trucks to pass, you also see parking cars in this street (I don't
know the German law, but they might be allowed to do that). What would
you do now? And if the parking allowance is time limited? For me lanes
is simply not applicable here.
--> I would tag the parking information with parking:lane, width, but
not lanes.
What I also propose: If lanes are marked, but narrow for trucks (e.g.
just 2m each), I would tag them width:lanes=2.0|2.0 now. If there is a
dedicated maximum width road sign --> maxwidth.
Though I'd think a road 4.3m wide would
fall under the 'lanes=1.5' idea
[...]
After reading through these emails I'm beginning to think the
lanes=1.5 would less confusing for narrow two lane roads.
-1
1.5 makes no sense. If we can agree that a lane is a "strip, which is
wide enough for one moving line of motor vehicles other than motor
cycles" (from the Vienna Convention of Road Signs, used as basis for
local law in many countries all over the world) -- then either one line
of vehicles can move -- or two.
--> For me this lanes=1.5 is a clear indication for an attempt to turn
the lanes tag into a rough width-estimate. I think the width tag is the
better tag for width-estimates.
martinq
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