Not sure I want to call it a round about as it was large with a city park and a couple of ball fields in the middle of it. It was designed to be a center piece (still is) of the city, and 4 streets (technically 8 streets since they all received east/west or north/south pre-fixes on either side of the circle) all perfectly intersect at 45 degree angles to each other. It's a full two lanes around the circle, so you can by-pass merging traffic if you know you're headed over half way around. It works great, but again, it's very large.
I've seen tiny partial 2-lane roundabouts and if the traffic is heavy they can be very difficult to navigate, especially for an out of town driver who isn't familiar with which lanes are circling and which ones have to exit.