Multi-lane roundabouts are problematic. If you have to change lanes in a busy roundabout it can be difficult to find a gap or have someone let you over. And if you're on an "inner" lane you will clearly have to cross the outer lane at some point to get off of the roundabout. I'm not talking about roundabouts that have a special lane for people turning right, which is helpful, but roundabouts that have two or more lanes in the main circle.