Roundabouts take up huge amounts of real estate.
You can accomplish the exact same result by just replacing the four “Stop” signs at an intersection with four “Yield” signs.
Yield to the drivers on your left, take the right-of-way over drivers to your right, just as with a roundabout and just as quickly.
But that would be far too simple and inexpensive.
Everything government does must be intrusive, expensive and of inferior quality.
It’s the law.
A four-way yield would rely on drivers knowing to yield to traffic from their right, which in turn requires that all drivers know left from right. That’s too much to ask, at least around here.
For at least a few years in the 90s, Highway 95 going north out of Las Vegas was a divided highway with a speed limit of 60. For several miles, the cross streets had no stop nor yield signs at all. It was amazing to see the cross traffic go sailing right across. I didn’t see any accidents myself, but broken glass (what a former girlfriend used to call “accident dandruff) was not uncommon in the intersections.
The only time I have had to deal with a double diamond interchange was in Las Vegas. I had never seen or heard of one, and I still don’t know how we got through it onto the right road. I haven’t been through Las Vegas in over five years, and I don’t care if I never have to again.