> They work where each direction has an approximately equal amount of traffic. However, usually, one direction (north/south, say) has a larger share of the traffic. In those cases, the bulk of traffic all needs to slow down, downshift, turn a bit in one direction and then turn a bit in the other direction for the minority of traffic that's bleeding on or off the main artery. In those cases, a traffic light is better because the timing can be adjusted to the proportion of traffic from each direction (and more flexible since it can be adjusted over time).

This point is so under-appreciated. Roundabouts are really good in some cases, but they're over-utilized in England. Imagine if the US had roundabouts on the interstate and you're getting close.

I think the main problem in England is that there is just too much traffic for too little road. I don't think there is a simple infrastructure solution to that problem.

For example I was going to point out that roundabout completely fail when one direction becomes nose to tail congested but when I thought about local examples, I'd rather take that over a set of traffic lights where it becomes near impossible to get out from one direction if the traffic keeps backing up onto the junction.