There is a running gag in the movie "The American President." The heroine is new to town and she's always running late. She cannot for the life of her figure out the traffic circles. What the nation's capital may want to try instead is a simple roundabout. Towns in the Charleston area have tried them out and are impressed with the results: fewer car accidents and many fewer accidents with injuries.

Both a roundabout and a traffic circle (sometimes referred to as a "rotary," too) take the place of a standard intersection with stop signs or a traffic signal. From the air, they both look like a bicycle wheel: Traffic moves in one direction around the hub, merging on and off the spokes. The idea is to keep traffic moving at a fairly steady pace.

A roundabout is different from a traffic circle in a few important ways, according to the Insurance Institute for Highway Safety. First, roundabouts are smaller. Second, vehicles make a sharper turn to enter a roundabout, and, as a result, speeds tend to be slower.

Third, because they are smaller, roundabouts don't have the multiple lanes of traffic, "yield to the right" confusion of a traffic circle. Signage and road markings direct vehicles to their exits, but, unlike a traffic circle, there are only two lanes of traffic to negotiate. The inside lane must move slowly because of the tight turn, so high-speed lane changes are less of a problem.

How does this all add up to safer roads? We'll get into that in our next post.

Source: Post & Courier, "Mount Pleasant's traffic loops help prevent accidents, gridlock," Prentiss Findlay, Nov. 28, 2011