If the description provided on the wiki is correct, it seems obvious that the fix can not be the modification of all roundabouts in OSM. I suppose that we also can not ask Garmin to publish new firmware, so the only solution seems to be in mkgmap.
If this forum is the right place to ask mkgmap’s developers, could you provide a workaround for this issue? If not, where would be the best place to report this issue?
This is a very old problem which I haven’t encountered for years. In general the answer is to map entrances & exits as separate nodes on the roundabout: not doing so allows routing to not touch the roundabout at all, which in turn means that correct time penalties are not added.
Unfortunately, this issue still happens in real life (at least for me): many roundabouts have no separator between entrance and exit, so there is only one node that connects the road and the roundabout. I will ask on the mkgmap developers mailing list.
I think there is no need to ask in the mkgmap list, this is a problem in the OSM data and should be fixed in OSM.
If you know a place where the OSM data is correct but the counters are wrong please provide a link to the osm object.
Unfortunately I do not own the Garmin router so testing is not easy (the actual user reported this issue to me), but I could try to find a problematic roundabout in the next weeks/month.
Anyway, I would like to make sure I understand the issue properly, so tell me if I am wrong: it happens each time an enter and exit share the same node to connect to the roundabout, for example on the West road of this roundabout. In this case, what should be changed on the map to make it correct?
If I am wrong, could someone explain it again? Thanks!
You understand correctly, though this roundabout doesn’t have an issue. The entrance from the north and the connection to Chemin de Saint-Bonnet are on separate nodes, so a user would have to traverse a small section of the roundabout to get between them. In this case, the user should be told to enter the roundabout and exit at the first exit. The issue arises when an entrance and exit share the same node, at which point a user can be routed directly from one to the other without having to use the roundabout. In such a case, the user would probably be told to simply make a right turn with no mention of the roundabout.