No one uses turn signals on them, and you never know when, where, or if someone is going to turn. It's haphazard maneuvering. 4-way stops are far more predictable and functional.
Your first comment is accurate, no one uses turn signals in any of the ones I use on a daily basis either, but that doesn't make them inefficient. In fact I think it keeps everyone on the defensive, and makes them pay more attention before entering.
But as I said in an earlier comment, the reason they kind of suck in the US is we don't seem to do them right.
* A very wide circle (350ft/100m minimum) with 3 lanes
* Each entrance and exit has 2 lanes.
* The outside lane of the circle directly connects the outside entrance with the "first" exit.
* The middle lane of the circle and the inside lane of the entrance allows you to exit at ANY of the exits
* The far inside lane of the circle exits nowhere without a lane change, but allows you to bypass an exit that might be backed up due to traffic.
Huh? That's only feasible for intersections of large roads, but American four-way stops are usually on small(ish) residential roads, where single-lane roundabouts work just fine.
No one is saying that roundabouts should replace ALL intersections, and the few they have in small residential places operate just fine with a single lane, but I'm skeptical of their value over a proper 4 way stop or a 4 way protect turn light.
