I don't see roundabouts as a replacement for traffic lights in the US. Above a certain traffic volume, you'll almost always want to move to traffic lights anyway. They're actually a replacement for the 4-way Stop - a ridiculous type of intersection that ought not to exist.
Or my personal favorite in Sacramento, roundabout with some stop signs sprinkled in. I hear horns and accidents daily... https://www.google.com/maps/@38.5801855,-121.4694376,3a,75y,...
Coming from Australia (that admittedly at times tends to over uses roundabouts) all i can ever wonder when i see a quiet road with traffic lights, or a seemingly pointless 4 way stop sign is "WHY IS THIS NOT A ROUNDABOUT?" I agree at a certain volume there are better alternatives, but there are massive benefits for a very long time and if you have the room for a large enough roundabout they can handle massive volume.
Here is a decent example that is just near Newcastle University in Australia. Traffic lights here would likely be much slower: https://goo.gl/maps/MPhri8vrt5M2
Side note: North America, please stop abusing using "stop" signs. No one stops anyway, just make them "Yield" signs unless its a seriously bad intersection.