Here in Seattle, if one wants to turn left at a traffic circle, one can simply turn left (effectively going the “wrong way” rather than going around). I had thought that was way illegal, but the city recognizing large trucks and whatnot may have difficulty moving around the “right way” so they allow everyone to make such left turns.
Also, traffic circles are the little circles meant to slow traffic on residential streets. Roundabouts are larger and are meant for improving traffic flow.