They are very common throughout New England. In other areas, also called round-abouts, or traffic circle I guess.
But amazingly, so many drivers fail to understand their simple design. They are far more efficient than traffic lights if everyone uses them properly. If in doubt, please consult this friendly diagram.
put one in my town, hardly any accidents before but a few houses complained about safety leaving their street despite a secondary exit 1/3 mile up the road. Town gave in and there have been a series of accidents, typically late night idiots forgetting the round-a-bout exist driving straight into the center island - that includes a police cruiser. I have watched idiots take a left into the rotary, and drive head first into traffic. People are fucking dumb