Over at OSRM we're not only doing Routing on OSM but also Guidance for users once a suitable route is found. In order to make the user experience great and the instructions pleasant to use we differentiate between
1/ Roundabouts Think: "at the roundabout take the nth exit" 2/ Roundabout Intersections These are roundabouts with up to four ways and turn angles which makes the turns obvious. Think: "at the roundabout turn left" 3/ Rotaries These are large and named roundabouts. Think: "at Meinplatz take the nth exit" 4/ Not-a-Roundabout (what this post is about) There are situations where one of the entering road has right of way, which disqualifies the scenario for being classified as a roundabout. The Wiki has a section on these Not-a-Roundabouts: http://wiki.openstreetmap.org/wiki/Tag:junction%3Droundabout#Not_a_roundabout > In all these cases, the key “junction” is not necessary at all. You need no special tagging. Most of these Not-a-Roundabouts have a note on them, telling users not to tag them as junction=roundabout as this is a common mistake. Here are two examples in Berlin: Bersarinplatz http://www.openstreetmap.org/way/288767318#map=19/52.51849/13.45355&layers=D http://www.openstreetmap.org/directions?engine=osrm_car&route=52.51786%2C13.45348%3B52.51918%2C13.45281#map=19/52.51852/13.45327 Kottbusser Tor http://www.openstreetmap.org/way/159155852#map=19/52.49898/13.41881&layers=D http://www.openstreetmap.org/directions?engine=osrm_car&route=52.49915%2C13.41952%3B52.49857%2C13.41852#map=19/52.49896/13.41865 As you can tell, for both of those situations the routing engine is not able to issue special instructions since there is no tag to parse. And parsing note tags for the occurrence of roundabout is not a solution ;) With the current situations of having note="don't tag as roundabout" pseudo-tags on most of those it would make sense to establish a proper junction=not_a_roundabout tag (tag is up for discussion) software can parse and make use of. What's your opinion on Not-a-Roundabout? Cheers, Daniel J H
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