https://www.openstreetmap.org/#map=19/40.71498/-74.01331

Divided roads like West Street in NYC seem to always be mapped as 2 separate one-way roads. When the divider ends, the 2 roads merge into one. I always thought this was a bit odd because it seems to contradict the "one feature, one OSM element" rule. In the case of a road it probably doesn't matter much, but it could for traffic signals. I've been thinking about how navigation software determines the best route to the destination. If it counts the traffic lights along the route, having 2 intersections with a divided road, each tagged as a traffic signal, would probably cause issues. Since the divided road is only divided between intersections and not through them, shouldn't the 2 halves of the road join at a single intersection node?

asked 17 Apr, 08:46

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tguen
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West Street is mapped as a dual carriage way since it is physically not possible to cross from one direction lane onto the other. Neither can pedestrians easily cross from one side to the other here.

There are different ways of mapping traffic lights. In your example an easy approach has been chosen. To map more accurately one could set the lights only on the incoming ways and/or use direction tags to indicate which direction the light is valid for. You can read up on this in the wiki, which gives a lot of different examples.

permanent link

answered 17 Apr, 10:26

TZorn's gravatar image

TZorn
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accept rate: 15%

Thanks for the link. I had checked the Key:traffic_signals page but not that one. The way it's mapped seems to be an approved method, however...

"Add traffic signals to the common nodes in the junction. It is up to the routing software to count nearby signals as one for timing purposes."

This seems like a bad idea to me, but I'll bring this up in the wiki page's discussion section.

(20 Apr, 00:30) tguen
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question asked: 17 Apr, 08:46

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last updated: 20 Apr, 00:30

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