I think you are making lots of assumptions here, like when I say space, I guess you assume it is still perfectly flat and the roads are perfectly aligned? The particular four way I'm thinking about, which really should be a traffic circle if they could blow away some houses, is 65th NW and 3rd in Seattle:
So notice we already have problems in a bad alignment of 3rd, and 65th is basically a steep grade, even coming up form the west. I think you could put a circle in if it were flat, even with the bad alignment (or maybe because of the bad alignment), but this hills make a non-starter. It also gets enough traffic that I'm pretty sure they are just going to put a stop light up eventually.
https://maps.app.goo.gl/7KBhbJ9oAvDwrfGN8
So notice we already have problems in a bad alignment of 3rd, and 65th is basically a steep grade, even coming up form the west. I think you could put a circle in if it were flat, even with the bad alignment (or maybe because of the bad alignment), but this hills make a non-starter. It also gets enough traffic that I'm pretty sure they are just going to put a stop light up eventually.