Mental tax is a feature, not a bug. Intersections are dangerous; the more attention you need to pay, the better. The biggest problem with light signals is that

Mental tax is a feature, not a bug. Intersections are dangerous; the more attention you need to pay, the better. The biggest problem with light signals is that they don't force you to pay attention. Normal-sized roundabouts usually have a big feature in the middle that you'll hit if you don't pay any attention.