What's the significance of roundabouts per square mile? It seems pretty meaningless if I'm honest. There's huge swaths of rural land where roundabouts are totally unnecessary.

There are also huge swathes of city, much like other countries.

At the same time, the US is much larger than most, so "There are 10,000+ roundabouts in the US" isn't very significant. A proportion would thus be a better metric here than an absolute number.

If you have numbers on intersections per country, and what proportion of them are roundabouts, that would be better, but I don't, so I'm using land as a proxy. I would also accept sum total road length as an option for denominator.