[Tagging] lanes = 0
osm at westnordost.de
Thu Jun 13 08:41:19 UTC 2019
> Here, legally, if there are no lane makings then it is considered to have one lane in either direction.
I am kind of a fan of lanes=0, denoting that there are no marked lanes. Here is why:
a. if a road with no lane marking is tagged as lanes=2, this situation cannot be distinguished from a road with 2 lanes
b. if a road with no lane marking is tagged as lanes=1, this situation cannot be distinguished from a road with 1 marked lane (a oneway road?)
So, in both these cases, the tagging is not explicit.
But it is important to be able to make the distinction. Some reasons:
1. Verifiability: Clearly, "on the ground", a road with 2 lanes looks different from a road with no lanes. A famous example for even a very broad road that has no lanes is Place Charles-de-Gaulle in Paris 
2. Legal implications: As far as I know, there are legal implications for roads with no lanes. Depends on the country of course, two examples that come to my mind:
2.1 In Germany, (afaik) it has implications when passing obstacles. If there are marked lanes, you can only cross into the other lane when it is free, while if there are no marked lanes, whoever reaches the obstacle first may pass first, independent on whose "side" it is
2.2 In China, the default speed limit if nothing is signed in towns is 50 km/h but on urban roads without a center line, it's 30 km/h 
3. Fuzzy/Implicit implications: Software may want to treat roads with unmarked lanes differently from ones that are marked. A few examples:
3.1 StreetComplete may want to ask surveyors to measure a road width in meters only for unmarked roads because they are likely very thin and the traffic throughput is not clear through the lane count
3.2 router software may want to slightly prefer roads with lanes>=2 over unmarked roads and/or calculate a virtual lane count from the given width, if any - especially if the maxspeed-tag is missing
3.3 map rendering software may want to render roads as they appear in reality. F4Map already does this rudimentary 
Now, my argumentation is in favour of making a distinction between unmarked and marked but not explicitly for lanes=0. I wouldn't mind or even slightly favor a tag like nolanes=yes or similar - this would be even more explicit. But since this does not exist (yet), lanes=0 would do as well in my opinion because it also reads as "zero (=no) lanes".
 see https://firstname.lastname@example.org,2.2942766,3a,75y,117.5h,85.1t/data=!3m7!1e1!3m5!1s4ofE9aRZMKKfWiiB2SiOrQ!2e0!6s%2F%2Fgeo1.ggpht.com%2Fcbk%3Fpanoid%3D4ofE9aRZMKKfWiiB2SiOrQ%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D203%26h%3D100%26yaw%3D166.38968%26pitch%3D0%26thumbfov%3D100!7i16384!8i8192
 see https://wiki.openstreetmap.org/wiki/Default_speed_limits
 see https://demo.f4map.com/#lat=53.5832254&lon=9.9338489&zoom=19
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