Although safety is the main reason that roundabouts have become popular, reduced delay, attractive appearence, and speed control are other reasons that roundabouts have been built. Roundabouts are not the best solution in every situation and are receiving careful consideration as part of the Northwestern Connector Project. People are often unfamiliar with roundabouts and skeptical about whether they will work. Roundabouts are often confused with traffic circles, which are viewed negatively because of congestion, high crash rates, poor entry conditions and high speeds. However, there are significant differences between traffic circles and roundabouts.
Diameter is calculated based on traffic volumes and movements and are much smaller.
Approaches are flared and deflected around the central island and speeds are constrained to 10 - 20 mph by design. Entering vehicles must yield to circulating vehicles. High speeds do not allow adequate gaps, for merging traffic and can cause a complete stoppage of traffic within the circle. Speeds can approach 50 mph. Traffic circles can be used successfully in low traffic situations, such as within a subdivision.