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Junction cloveleaf.jpg

This is a proposal for a set of tags and members making a Relation to group the ways and/or nodes comprising a road junction. The main purpose of the Relation at present is to give renderers or route planners a name and or number for a junction. It also means that a staggered cross roads controlled by linked traffic signals can be grouped into the one junction while still maintaining the geometry of the streets correctly. I can see it possibly developing in time to be a place where other aspects of the junction can be modeled.

Need for a relation

For a simple crossing where 2 ways cross each other at a single node it is not necessary the use a relation. It is obvious that the only the node where the 2 ways cross is part of the junction. The need for a relation occurs when there are ways and or nodes which could be considered part of 2 or more ways. An example would be a dual carriage way crossing a single carriage way. The piece of way between the dual carriage way and also the intersecting nodes could be considered part of both ways.


Key Value Discussion
type junction
junction SeeProposed features/Junction link is for clover leaf and similar type junctions; just omit this tag for junctions like cross-roads and simple single-bridge motorway junctions (unless someone can suggest a vocabulary for them)
name a name if the junction has a name (e.g. "Charlie Brown's Roundabout")
ref a reference if the junction has a number (e.g. junction 10 on a motorways would be "10")


Way or Node Role Recurrence? Discussion
Way Node (blank) one or more the ways and/or nodes comprising the junction (a typical grade separated motorway junction would combine ways, but a simple cross roads only has a node comprising it. A single carriageway crossing a dual carriageway might include the two nodes and the link between the carriageways in the junction.
Node label optionally one a hint to a renderer as to where a good place to put the the junction number or name on the map