I've noticed sometimes the OSRM router gives odd directions through a roundabout. Is this a bug in the router, or is there something wrong with the tagging?

For example, here, the directions are to "take the exit onto WA14", rather than to "take the second exit onto Washougal River Road". And again here, same error for a different starting point. But this route recognizes the first exit and counts it.

Similarly at this nearby roundabout, all three routes exiting to the South give bad directions, while the routes exiting north are described as expected.

Is this something I've tagged wrongly? I can't see any difference between the ones that work and the ones that don't.

asked 30 Aug, 22:33

noliver's gravatar image

noliver
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edited 30 Aug, 22:35

I think the first two examples don't count the first exit as the roundabout section as the same name as the lead in road and OSRM believes to be on the same road so does not count it. I am not sure if roundabouts should have the road name. What if two major roads met at a roundabout, what name would you give to the roundabout? the first or the second?

(2 days ago) andy mackey

It does seem likely that some router packages may be confused by the circular ring having the name of one of the streets, as andy mackey suggested. The wiki page for the junction=roundabout tag https://wiki.openstreetmap.org/wiki/Tag:junction%3Droundabout#How_to_map says this about naming:

"Give it a name only if is official or displayed (generally it is different from the name of highways connecting or passing though them, but many of them remain unnamed as it is undecidable between these competing highways, and because there's no address for residents located inside, or because addresses are given to one of the connecting highways: only large roundabouts have a dedicated name)."

and this:

"Again, a roundabout should only be tagged with name=* if the junction itself is named independently and differently from the roads crossing it."

(2 days ago) yesimlost

I don't think there is anything wrong with the data. Looking at the tags I don't see anything out of the usual and there are other routers that generate correct turn by turn instructions, even other OSRM instances. There must be something wrong with the OSRM implementation used here. You could open a ticket on Github to address the issue there.

These are working fine for example:
map.project-osm.org
Graphhopper on openstreetmap.org

OSRM on openstreetmap.de is doing it wrong again.

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answered 03 Sep, 10:04

TZorn's gravatar image

TZorn
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accept rate: 12%

Thanks. I've done some more research and opened an issue here: https://github.com/Project-OSRM/osrm-backend/issues/5554

(2 days ago) noliver

When you switch the router to Graphhopper, you will notice that that router numbers the exits. So there is nothing wrong with the data.

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answered 2 days ago

escada's gravatar image

escada
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accept rate: 21%

I have looked at the data and the one way sections into and out of the roundabouts have turn restrictions which i don't think are needed, oneway on the road should do the job. They may be the problem. I also think giving the roundabout the name of the road may be causing a problem OSRM may use logic that assumes the roundabout as a continuation of the road so doesn't count it, and therefore second exit is reduced to the first, maybe? This one in Peterborough UK ( we drive on the wrong side here) works in the 3rd exit type description. and does not have the turn restrictions mapped, or naming issue. It just as one way on the one way sections. https://www.openstreetmap.org/directions?engine=fossgis_osrm_car&route=52.6011%2C-0.2081%3B52.5981%2C-0.2147 I don't think OSRM directions are good either, They are confusing.

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answered 02 Sep, 17:22

andy%20mackey's gravatar image

andy mackey
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edited 2 days ago

The only turn restrictions I see are forbidding u-turns where the carriageways split into entry and exit ramps (unless someone edited anything in the meantime). I don't think they should influence the instructions for leaving the roundabout.

(03 Sep, 10:07) TZorn

Her's one of the turn restrictions, in my opinion the one way section means the turn restrictions are not needed. https://www.openstreetmap.org/node/6742527237

(2 days ago) andy mackey
1

I see what you mean--I wouldn't have created those manually in JOSM, but the ID turn restriction editor sort of implies that this restriction may be desirable, since without them, it shows a possible u-turn from the two-way street back onto itself instead of continuing on to the one-way portion. I think it's unlikely any router would try to use that route with the roundabout just ahead, so you're probably right that they're unnecessary, and I won't make a habit of creating them, and may come back and remove them once this issue is resolved.

In this specific case, they are not present at the adjacent roundabout where OSRM also has issues, so I don't think they're the root of this issue.

(2 days ago) noliver

Looking at satellite images for the intersections mentioned by the original poster, these look like ordinary four-way crossings, not roundabouts. Were these recently redone as roundabouts?

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answered 2 days ago

yesimlost's gravatar image

yesimlost
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2

The mapper (noliver) does say, in the edit, new roundabout.

(2 days ago) andy mackey
2

Yes, these were both installed in the last 3 months, the first in early July.

(2 days ago) noliver
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