I’ve heard that the District’s traffic circles aren’t roundabouts—what’s the difference? And what’s the biggest circle in the city? And the smallest?

D.C.’s circular intersections are considered traffic circles since they feature stop signs or signals and give priority to entering vehicles. Roundabouts force vehicles entering the intersection to yield. They also use both pavement markings and raised islands to direct traffic into a one-way counterclockwise flow to prevent confusion, as well as to slow traffic. Since roundabouts force traffic to slow and create gaps in traffic, roundabouts are safer than circles—as well as the stop signs or traffic signals they replace—according to a 2001 study by the Insurance Institute for Highway Safety.

One reason that the District features circles rather than roundabouts is that modern roundabouts did not emerge until 1904 in New York City—nearly 113 years after Pierre L’Enfant designed the District’s street grid featuring wide avenues radiating out of traffic circles.

The varying size of the District’s avenues creates a wide range of traffic circle sizes. For instance, Plymouth Circle in Colonial Village is only 95 feet across due to its isolated location between Rock Creek Park and Beach Drive in the northern corner of the city. Likewise, both Garfield and Peace Circles measure about 150 feet due to their locations on the National Mall. The largest circle, the 2,100-foot diameter Observatory Circle, no longer exists—at least as a circle—since the intersection of Massachusetts Avenue and 34th Street now forms an arc to isolate Dick Chaney’s digs at One Observatory Circle. As a result, the Lincoln Memorial Circle now holds the title of the District’s largest circle with its nearly 700-foot diameter.

Every Monday, the ‘Huh?’ Bub takes your questions. Got one?