One issue with dual carriageways (and now I think about it, also railway lines) is about generalisations at certain zoom levels. If you zoom out beyond a certain level, both halves of a DC (or the individual tracks of a railway) would be better modelled as a single line. The renderer/consumer needs an algorithm, and/or hints from the tagging, to know what belongs to what. Often a DC is very recognisable as two one-ways in opposite directions with the same name/ref and "more or less parallel", but I imagine it's that last bit which can cause problems if the roads are not reasonably straight.
On the subject of man_made=bridge, that relies on geometry to associate the parts. That loose association only works because bridges are straight(ish). No need for relations where there is no need for them? Sounds a bit like a circular definition. If a relation is the right way to model reality, we should also not run away from them. They can provide certainty where otherwise complex heuristics would be needed which may or may not work in all cases. Two streets with the same name isn't good enough on its own IMHO. The two halves of a dual carriageway may have different names and still be the same road. //colin On 2015-11-24 12:17, Martin Koppenhoefer wrote: > 2015-11-24 11:45 GMT+01:00 Colin Smale <colin.sm...@xs4all.nl>: > >> So has the "street" relation just been born? It could solve some other >> puzzles as well: dual carriageways, cycle tracks, bridges... > > bridges have been solved by introducing a revolutionary concept: a dedicated > object for an explicit bridge. It remains a mystery why it took us 10 years > ;-) > Have a look at man_made=bridge, doesn't even require relations. > > The "street relation" has not only been born, it has already died, at least > almost. Like its cousing, the associatedstreet street (which seems more live > than the street relation). Honestly, I don't understand what these relations > could solve in conjunction with dual carriageways, could you explain? > > Generally we should avoid relations where they are not necessary. No need for > a relation to say these street parts do share the same name. Simply put the > same name on them. > > Cheers, > Martin > > _______________________________________________ > Tagging mailing list > Tagging@openstreetmap.org > https://lists.openstreetmap.org/listinfo/tagging
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