Besides roundabouts often being bigger and more unpleasant to cross for pedestrians than an equivalent traffic-light junction, roundabouts have a sweet spot - l

Besides roundabouts often being bigger and more unpleasant to cross for pedestrians than an equivalent traffic-light junction, roundabouts have a sweet spot - low to moderate traffic, and sometimes heavy traffic when there's a balance of exit usage. When not all exits are used frequently, heavy traffic can starve entrance from roads whose exits are not used. Exiting traffic frees up a gap for entering traffic to use. If there's nobody exiting before your entrance, you don't get to join. Traffic lights are sometimes added to roundabouts to patch this.