From article:
Roundabouts (AKA rotary or traffic circle) have gained popularity in Europe and more progressive areas of the US like Seattle in recent years. By eliminating a four-way stop intersection and replacing it with a roundabout you allow for the continuous flow of traffic. This not only greatly reduces the unnecessary additional emissions from repeated start-stop cycles but it also reduces vehicle noise and reduces the number of accident opportunities.
http://www.triplepundit.com/pages/askpablo-well-to-wheel-efficie-002467.php
