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When I'm putting together a road route relation which goes via a roundabout but which traverses less than 360° of the roundabout, is it better A) to split the roundabout and add the appropriate fragment to the route in a similar way to what one would do for other, non-roundabout, road sections where the route diverges, or B) to add the roundabout as a single looped way to the relation?

asked 07 Feb '11, 12:31

Andrew%20Chadwick's gravatar image

Andrew Chadwick
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accept rate: 25%


I don't think there is a hard rule, but I tend to prefer having the roundabout as a single looped way.

I'd rather keep the roundabout whole if possible. It makes it easier to move it around or form it into a circle. It also seems less likely to confuse mapping/routing apps, which may treat multiple ways tagged roundabout as multiple roundabouts.

I don't think it is a problem if a bus route is shown to go all the way around the roundabout rather than just between the entrance and exit, especially if it is a fairly small roundabout. And bear in mind that if the bus makes the return route in the opposite direction then it will use all of the roundabout anyway.

Having said that, I wouldn't go and fix this if I saw other OSMers had mapped it as separate ways.

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answered 07 Feb '11, 17:23

GrahamS's gravatar image

GrahamS
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accept rate: 28%

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I think I'm the same. I think better to keep it as a single looped way, but I'm unlikely to go and change this if someone did it the other way.

I did wonder if this question is related to the relation checker, as it thinks the route might have a break in it if it goes through a roundabout. Even so, for the same reasons as above, I'd tend to keep it as a single looped way.

(08 Feb '11, 01:57) Ebenezer
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@Ebenezer more of a general question really. I can see reasons for doing it both ways, but I'm tending to favour option B) right now despite having done A) in the past myself (not a reason to go back and "fix" of course).

One of the important factors is maintainability. Relations are fairly tricky at the best of times, and a heavily split-up roundabout with diverging feeder oneways and crossing routes can be a pig to maintain if people are adding purely geometric splits and changes for other reasons. Making the data less fragile, or less liable to be broken by editors is a Good Thing™

(08 Feb '11, 12:38) Andrew Chadwick
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Software treating multiple ways tagged as roundabouts, as multiple roundabouts, is in error; roundabouts can be, for example, partially on a bridge=* - i.e. one main road passes under the roundabout. And lane counts can change within the roundabout. One way: good start - many ways: more detail.

(13 Feb '12, 11:37) alv
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As @alv pointed out, there are many more reasons to split the roundabout way. Any routing application should be able to use split roundabout added correctly to relation.
The bus does not always go the same road back and it obviously does not circle around, which makes it incorrect. Of course still better one way than nothing.

(13 Feb '12, 18:08) LM_1
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It is better to split the way of the roundabout to better reflect reality. Roundabouts are one way streets, and a bus route even goes on different streets depending on the direction.

Sooner or later the roundabout will be split into parts anyways, because other attributes (lit, lanes, maxheight, enforcement, restrictions, etc.) are different, too.

Do not map for other persons comfort. Map reality.

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answered 09 Feb '11, 12:28

Kartograefin's gravatar image

Kartograefin
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Of the two options, I would pick A.

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answered 07 Feb '11, 16:41

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Derick Rethans
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question asked: 07 Feb '11, 12:31

question was seen: 8,458 times

last updated: 13 Feb '12, 18:08

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