[JoeAltmaier]

Roundabouts are extremely sensitive to rates of traffic. If one direction occasionally fills from e.g. a school parking lot, the others can become instantly congested.

You can use traffic lights etc to fix this. But then the major benefit of roundabouts is extinguished: their cheap cost. Just some pavement and acres, painted lines.

[ryandrake]

They're great for low traffic neighborhoods where the intersections don't warrant something as heavy weight as stoplights or 4-way stops. I'd love to replace every ridiculous 4-way stop in my neighborhood with a roundabout, it would probably double the life of my brake pads and have no effect on safety. Except Americans are baffled by them and they'd probably get shouted down at the next city council meeting for being weird and confusing.

[SoftTalker]

I have thought that a "zipper merge" (let one car in ahead of you) convention would help congested roundabouts but that isn't how we're taught to use them.

[ghaff]

I'm not sure how that would work. Now the person entering the rotary has to trust that another driver isn't going to cut them off. I can tell you that merges right after a traffic light it is absolutely routine for a car (or probably more likely a pickup) not to let you alternate. I don't even bother with the FU horn any longer.