The difference between a (modern) roundabout and traffic circle is more semantical, and has become the preferred name for a specific kind of traffic calming.
Although, a traffic circle can very easily not be signaled. Mass and NJ both have non-signaled circles (or rotaries as they are called in Mass). In DC, both Grant and Sherman Circles are not signaled. And most of us would refer to them as traffic circles. As would most Brits, who also generally don't have signals on their traffic circles.
Here is a nice definition in terms of what a roundabout does in terms of traffic calming (versus a traffic circle that is designed mostly to move traffic through quickly).
With Gersin, Turkish and Harris v. Oakland County Road Commission having been ruled in Federal Court, March 2008, in favor of the plaintiffs, that un-signaled roundabouts violate the Americans With Disabilities Act, the distinction between roundabout and traffic circle becomes largely moot.
Grant and Sherman Circles are perfect examples of L'Enfant's intent, and show full-sized traffic circles that haven't been chipped away by the addition of additional road lines (compare to Dupont Circle).
You know, the traffic around Dupont doesn't bother me.
In fact, I think the ambient noise it provides once you're in the park adds to the experience, rather than detracts.
... That's not to say the pattern of lanes around Dupont couldn't be better. Sure it could.
Just that there's a case where lots of cars don't themselves hurt urbanity.
Personally I find traffic circles in MD very frustrating because the VAST majority of people have no idea how to handle it and who should be yielding to whom.
Perhaps the MVA should require traffic circles on the license test for new drivers and require new residents to be able to demonstrate they know what to do a a circle.
Commenting by HaloScan
