Some terminology about circular traffic features: Big things that you can travel quickly into, which are most commonly found on the U.S. East Coast (e.g. Washi

Some terminology about circular traffic features: Big things that you can travel quickly into, which are most commonly found on the U.S. East Coast (e.g. Washington, D.C.) are called rotaries, and are generally considered to not be particularly good or safe. Mid-sized things with splitter islands preceding the entry, and that have an angle of entry that prohibits entering at speed are called roundabouts, and generally are considered a good thing from a speed / efficiency perspective. Small things with no splitter islands preceding, that are usually put on quiet residential streets (common in Seattle among other places), are called traffic circles. Confusingly, rotaries are sometimes called traffic circles too (see Dupont Circle). I disagree with your assessment about traffic circles being placed by city meddlers, as well as the assertion that they don't have a positive effect on safety. First, in Seattle and elsewhere, they are typically requested by residents of the street (not us meddling urban planners), and are built where a speeding problem is confirmed, as resources become available, and according to some geographic equity criteria. Second, though I haven't done an exhaustive review of traffic circle literature, this summary review article is bullish on traffic calming features generally, and specifically on traffic calming circles as well: http://jpl.sagepub.com/content/23/4/347.short http://jpl.sagepub.com/content/23/4/347.short