The only double diamond I routinely encounter (and just realized that’s what it was) is around an interstate interchange. With the scale of the interstate traff

The only double diamond I routinely encounter (and just realized that’s what it was) is around an interstate interchange. With the scale of the interstate traffic, roundabouts would be difficult to use. Difficult, but not impossible… I’ve also used roundabouts over highway traffic, but not with the same throughput of traffic that interstates have.