Mist, die Stelle hatte ich übersehen. 18.5.12
https://wiki.openstreetmap.org/w/index.php?title=Tag:junction%3Droundabout&direction=next&oldid=772094
A roundabout is a one-way street with right-of-way and a non-traversable centre island. There can be traffic light, as long as the circular road has right-of-way when the lights are off.