I sometimes think that we need a translation service, from US English into British English, on AB ;-)
In the UK we don't have 'traffic circles'; we have 'roundabouts'. Rather than being there to slow traffic down, their purpose is meant to be to speed it up! Or, more accurately, they exist to improve the flow of traffic without the use of traffic lights. (If there was a simple 'cross roads' junction, a constant flow of vehicles in one direction could prevent other vehicles going across that flow. The use of a roundabout introduces gaps in the traffic flow, to give all motorists the chance of getting across the junction).
The first circular flow of traffic (effectively a 'traffic circle' or 'roundabout') was introduced around the Arc de Triomphe, in Paris, in 1901. (It's still there, and with modern traffic flows, it rates as one of the most terrifying road systems anywhere in the world!). New York followed with the Columbus Circle traffic system in 1904, which is rather more like a modern traffic circle. When England's first 'garden city' (Letchworth) was built to house the 'London overspill', we acquired our first roundabout (in 1909).
More on Wikipedia, here
http://en.wikipedia.org/wiki/Traffic_circle
and here
http://en.wikipedia.org/wiki/Roundabout
Of course, we Brits can't just be satisfied with simple roundabouts. Many of our towns and cities now have so-called 'magic roundabouts', comprised of a set of roundabouts in a ring. Those who use them every day usually find them fairly easy to navigate, but strangers often have great difficulty in selecting the correct lane for their exit!
22:30 Fri 08th May 2009