Supposedly, "roundabouts" (which we grew up calling "rotaries") were incorporated to the city's layout for defensibility. But, that's just reliance on a bit or lore from a high school Am. Hist. teacher. Control the "roundabout" and you have control over the arterials that feed into it.
[N.B. There are technical distinctions between roundabouts, rotaries, traffic circles, etc.]The problem with "circular intersections" in the US is most folks encounter them so infrequently and with such trepidation that they make those drivers unsure/nervous when they *are* encountered. Most folks growing up with them take them in stride -- just like an on-ramp to a freeway, etc.
Statistically, they enhance safety at intersections for which they are appropriate.
There were a couple of (larger) traffic *circles* near one of my residences in MA that routed traffic effortlessly at freeway speeds. No one ever complained about entering/exiting them.
Here, we have some *stupid* intersections that look like an *excuse* for a circular intersection: a central hub that is barely a few feet across crammed into the center of a traditional intersection! I.e., all it does is force folks in each direction to veer off to the shoulders of each road to avoid whacking their inner tires on that "hub". And, gives all traffic the right "not to stop". Here, we have