
Wired ran a good article about this.
"Several years ago, Monderman ripped out all the traditional instruments used by traffic engineers to influence driver behavior - traffic lights, road markings, and some pedestrian crossings - and in their place created a roundabout, or traffic circle. The circle is remarkable for what it doesn't contain: signs or signals telling drivers how fast to go, who has the right-of-way, or how to behave. There are no lane markers or curbs separating street and sidewalk, so it's unclear exactly where the car zone ends and the pedestrian zone begins. To an approaching driver, the intersection is utterly ambiguous - and that's the point."
http://www.wired.com/wired/archive/12.12/traffi
When I left you, I was but the pupil. Now, I am the master. - Darth Vader