I've heard that that is why roundabouts are safer than their alternatives: counterintuitively, they're safer because they're less safe, forcing the user to pay more attention as a result.
One-lane-roundabouts are very safe. I lived in Hannover (Germany) in the 80s and 90s, they had 2 or 3 lanes in the roundabouts. There were large signs that counted the accidents (200+/year) to raise awareness and during the trade fairs (anybody remembers Cebit?) the number of accidents peaked. Today they are all a lot safer because of a lot of traffic lights.
Same with driving in the winter. Anecdotally I always observe more accidents when the roads are clear.
>they're safer because they're less safe
Roundabouts are safer. They're safer because they prevent everybody from speeding through the intersection. And, even in case of an accident, no head-on collisions happen in a roundabout.