Americans are too stupid to use traffic circles (roundabouts). They've been succesfully used for many decades in the UK.

Actually they're not. Roundabouts simply are foriegn to most Americans because in the past we, unlike the UK, have had the space for "cloverleafs" and other land-intensive solutions. We haven't had the need to use other solutions.

There are roundabouts in use in Howard County, Maryland; Washington, DC; Indianapolis, Indiana; and many other places. We usually call them "circles."