What is a... roundabout?

Coming from Ireland where roundabouts are a quite common sight at your daily commute I was surprised to see that the US went an entirely different way when it comes to traffic control. Traffic lights are more common here than anywhere else I went so far. Even in Germany it is easier to step over a roundabout from time to time ;-) But in several communities over here you can find them if you look hard enough...

Interesting is how different towns and cities explain those to the public over here. One of the more innovative ways I found in Steamboat Springs... a 'traffic circle' apparently is a little one way street spanning around a little circle... or simply a roundabout :-P