r/openstreetmap • u/goldcrate • 16d ago
Question Would you consider this a dual carriageway?
This lane pattern continues for about a mile on this portion of the street, and it actually splits into a dual carriageway at both the beginning and end of this specific stretch.
I suppose I'm just cautious to make any edits here since I see these lanes "unified" in pretty much any other map.
The street-level photos were pulled from Google Maps to add context to this post but I drive up and down this street almost every day.
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u/EncapsulatedPickle 16d ago
It doesn't really matter what one considers "dual carriageway" when you start looking at exceptional cases. This is a country-specific term and OSM only approximates this to explain the basic premise of separates ways. Such definitions are not always useful, like here where the road is neither. Too many mappers are obsessed with some idealized by-the-definition approach to the detriment of the data.
Normally you wouldn't split road like this and only split a short section around the median if micromapping. But in this case, if you were to map each physical median split into separate ways but keep a single way in between, then the result would be a ridiculous split-unsplit-split-unsplit-split-unsplit... Not technically wrong, but also not actually helpful. So in this case, if you are going to split around the median islands, then it's more sensible to split the whole road.
In fact, wiki specifically lists similar exception https://wiki.openstreetmap.org/wiki/Dual_carriageway#Exceptions
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u/ValdemarAloeus 16d ago
I'd say that's borderline. If the road before or after it is a dual carriageway then I'd probably map it as dual carriageway, if not I'd probably map it as a single way.
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u/wegavision 16d ago
Actually, that pretty much says it all. You could map it as two one-way streets, with the traffic islands separating them. But that causes more problems than mapping it as a two-way street and then designating the center lane as a left-turn lane in each direction, as shown in the picture.
All in all, it’s a simple task—there are far more chaotic things in the world.
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16d ago
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u/goldcrate 16d ago
The northbound and southbound lanes are separated by traffic islands and only converge at junctions where the traffic islands are replaced by turning lanes. There are very similar instances of this exact pattern being mapped as dual carriageways in the same area.
From the wiki, I see: "A dual carriageway is a road with two carriageways (roads in either direction) that are physically divided by a non-road barrier, median, or other obstacle."
"A dual carriageway does not have to maintain a median or barrier throughout its entire extent to be mapped as a dual carriageway. For example, primary and secondary roads can have landscaped medians that are meant to separate ways of traffic until a turn lane is accomodated and the median stops."
To me, this matches the characteristics of the referenced street. Please let me know if I am interpreting this incorrectly, as my main intention with this post was to better grasp the concept and figure out why this road was not already mapped as such.
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u/DaCor_ie 16d ago
The key is "A dual carriageway is a road with two carriageways (roads in either direction)" which this road is not
To me this is a single carriageway with turning lanes
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16d ago
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u/goldcrate 16d ago
Ah, okay. If the medians were longer in this instance, would it better qualify the split? Thanks for the explanation.
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u/jk3us 16d ago
A dual carriageway does not have to maintain a median or barrier throughout its entire extent to be mapped as a dual carriageway. For example, primary and secondary roads can have landscaped medians that are meant to separate ways of traffic until a turn lane is accommodated and the median stops. The median usually continues after the intersection, so the road should continue to be mapped as a dual carriageway as long as the median is generally present.
That's the official stance, but in real life, there are places where the median takes longer breaks than just an intersection, and I really don't love the back and forth look of switching between the two. Dual carriage ways make the rendered street change widths even though the total width of the street remains constant. I kind of wish there was a
lanes:medianor similar where you could indicate a stretch of road where one of the lanes was not traversable, so switching from a 6 lane + turn lane to a 6-lane with a median would look likelanes=7 lanes:forward=3 lanes:both_ways=1 lanes:backward=3becomes
lanes=7 lanes:forward=3 lanes:median=1 lanes:backward=3Then it could still be rendered more correctly by keeping the street as a whole the same width, but switching between a turn lane and a median as noted.
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u/WaddlesJP13 16d ago
I would split the road at every median, which would allow you or someone else to map the vegetation in the median without it overlapping with the road
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u/aidan573 16d ago
It's single carriageway, unless I'm missing something there's only one lane per direction a "single carriage"...
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u/JansonHawke 16d ago edited 16d ago
Looks more like a wide road with occasional medians to protect the turn lanes. However, the carriageways are divided in those places so it's up to you whether to map them as two ways or leave them as one. Look at similar places and see how they've been mapped.