As the current Republican presidential primary attests, perhaps it's because we prefer fascistic robots.
Why Does America Hate Roundabouts?,by John Metcalfe (City Lab)
Maps and data visualizations show the U.S. trailing much of the world when it comes to traffic circles.
Some argue the primitive roots of the roundabout actually grew in the U.S. “It’s widely accepted that William Phelps Eno was the bright spark who first devised the idea of a one-way rotary system in 1903, for Columbus Circle, New York City, USA,” asserts the U.K. Roundabout Appreciation Society, an organization rabidly opposed to “fascist, robotic traffic lights.” So why has the country fallen so far behind in deployment, given roundabouts’ elegant simplicity and proven safety benefits?
There are a lot of possible answers, says Lee Rodegerdts, an international roundabout expert (yes, they exist) at the Portland transportation-engineering and planning group Kittelson & Associates.
“My guess is that the possible benefit of roundabouts wasn’t widely known, and we had a long history of using traffic signals,” he says. “It took some bold people—both on the elected-official side and on the transportation-professional side—to get the first ones installed, and they deserve a lot of credit for sticking their necks out there. This boldness had to be repeated a lot around the U.S. during the [first] decade or two, given the skepticism of: ‘Well, that might work there, but it won’t work here.’”