[OSM-talk] Obvious turn restrictions

Nathan Edgars II neroute2 at gmail.com
Fri Jul 8 06:40:40 BST 2011


I've come across a fair number of what I call obvious turn restrictions. 
Here's an example: http://www.openstreetmap.org/browse/relation/1566983
The only thing being prevented by this is turning right onto Shelbyville 
Road from the motorway_link. But there's a cutoff to the southeast that 
you obviously take if you want to turn right.

So what's the point?
Any halfway-decent router will take the obvious route.
Even if a router doesn't do that, it should be clear to someone 
following directions that to turn right they need to take the 
island-separated right-turn lane(s).

The downside is that these relations lead to clutter, both in the number 
of times a way is split and the number of relations on a way. To give 
full restrictions at a simple intersection of two undivided roads with 
four island-separated right-turn lanes, one would need to split each 
road into at least four ways and create twelve relations.



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