I would agree, but my father used to drive a bottled water delivery truck. And he's seen lots of neighborhoods where roundabouts are simply not built large enough to accommodate anything with more than two axles. In California, roundabouts tend to be added into new construction, but squeezed into a space that is no larger than a normal intersection.
If they're designed properly, they should be low, almost the same height as speed bumps. That way something with 16 wheels can go straight over them while regular cars will probably go around them.
