# Talk:Relation:dual carriageway

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## Assymmetry

What do I do if there is a dual carriageway where there are no two "symmetric" ways?

Example:

```-----+----------------+------
-----+--------+-------+------
|
|
```

Wouldn't it be better to collect all the ways of the two roads in one relation? Something like

Way or Node Role Recurrence?
carriageway1 one or more
carriageway2 one or more

--Wabba 13:06, 24 October 2007 (BST)

Why restrict this to dual cariageways? How about multiple cariageways. E.g. where there is a dual cariageway through way in a build up area and side cariageways with multiple junctions. Like here: [[1]] --Cartinus 02:45, 26 December 2007 (UTC)

yes, i remember lots of these in melbourne, australia as well. would be very useful Myfanwy 12:47, 23 May 2008 (UTC)

this would be great to use for train tracks also. they are usually in pairs, but group together under one name Myfanwy 12:47, 23 May 2008 (UTC)

Sounds like it would make sense for the roles to be not literally defined, but still present. That is, roles could be "east" and "west", or "north" and "south", or "inner" and "outer". Or maybe, "north local", "north express", "south express", "south local" for a "dual-dual" setup. As far as the relation definition is concerned, the only requirement is that the relation have ways in at least two distinct roles. Multiple member ways can have the same role if they form parts of the same carriageway. Vid the Kid 03:16, 13 July 2009 (UTC)

Roles of "left" of "left<N>" vs. "right" or "right<N>" would get my +1. I agree that it's silly to require exactly two ways in one of these things and then have to repeat yourself a few tens of metres down the road: just use the relation for the entire dualled stretch and use the roles to keep track of which physical carriageway something is. --achadwick 14:54, 5 June 2011 (BST)

## Highways

What about more than two carriageways, or two carriageways and two cycle tracks that are part of the same highway? --Tessarakt2 13:02, 8 July 2008 (UTC)

## Lateral roads

What about lateral roads? In Brazil it is not uncommon that when a dual carriageway passes a populated area, it branches into lateral roads with a lower speed limit, and all the intersections to the populated area. They have almost always the same name/ref as the main dual carriageway, and only referred to as "Rua Lateral" meaning "Lateral road". --Skippern 13:08, 15 December 2008 (UTC)

## see also

I added a see-also -section as many dual carriageways are motorways that are already in a Relation:route-relation and that relation features roles for both directions in the general as well as the route=road -case. --MarcusWolschon 11:53, 15 April 2009 (UTC)

## Names and Labels

It's easy for a human to look at a dual carriageway and know where to write its name in the middle. But how do you tell a computer how to do that? Coming up with a good algorithm would be difficult. On the other hand, we could have another way along the approximate center of the dual carriageway, and its role in the relation could be a special value like "label". The relation can have name and/or ref values, which can then be used to produce an appropriate label for the whole dual carriageway. If the renderer is aware of this relation and does apply a label for the entire dual carriageway, it can then suppress rendering of name and ref labels on the member ways to avoid duplication. Vid the Kid 03:16, 13 July 2009 (UTC)

## Is this de facto yet?

I've added a taginfo/ValueDescription block to the main page which demonstrates that here are 997 uses of this right now in the db. Does this make it a de facto tag yet? :) If so, someone needs to determine how it's actually being used and document that. I've asked in the OSM Help Forum whether anyone's actually consuming this data. --achadwick 14:59, 5 June 2011 (BST)