The only roundabout (a "rotary", since it was in Massachusetts) that I ever liked was over a highway. Three roads intersected at the same point, with one being

The only roundabout (a "rotary", since it was in Massachusetts) that I ever liked was over a highway. Three roads intersected at the same point, with one being a divided highway. (each at 60 degrees to its neighbors, like a six-pointed asterisk) The solution: Make the roundabout really huge (probably safe at 70 MPH if you don't mind speeding tickets) and place it over top of the highway, crossing on two separate bridges. Provide ramps for the highway, and connect up the other roads as normal. Offramps from the highway are ascending, helping to slow vehicles. Onramps to the highway are descending, helping to bring vehicles up to highway speed. This turns out to be really really nice.