I was a member of several regional planning commissions who were responsible for dealing with traffic issues when these things were coming into vogue. Roundabouts are not meant to function as a large traffic circle. They are classified as "traffic calming devices" (similar to speed bumps) meant to keep traffic flowing at a slow but steady pace. We had some fairly major roads where rush hour traffic backed up severely due to several traffic lights. Once the lights were replaced with roundabouts, the backups were mostly eliminated...once people got used to them. There's a also an environmental benefit because slow-but-steady moving cars create less emissions than the same number of vehicles in stop-and-go mode.

Do a search for "roundabouts," and you'll find articles saying how great they are. Judging by the new ones in Kingston, NY, they aren't great.

We used to have a large traffic circle by the Thruway entrance. Four roads fed into it, and it was large enough that you could enter even if a car had just entered on your left. The new one - a roundabout - is so small that 18-wheelers must use both lanes. If you're waiting to enter, and a car enters on your left, it's too close for you to drive into the circle. The result is a line of cars waiting to enter the roundabout. As if that weren't band enough, cars in the left lane are allowed to make right turns to exit in front of cars in the right lane.

Now we have a brand new roundabout. We used to have traffic lights. Red - stop; green - go. Now we have this confusing roundabout, which people are avoiding by driving out of their way by several miles. I'm glad I found this picture so you can so what it's like. Of course, from the air, it's easier to get a good view and understand it. Down on ground level, with cars entering from every angle, it's very confusing.