Which roundabout configuration is noted for giving the worst performance?

• A. 1 entry lane and 1 circulating lane
• B. 2 entry lanes and 1 circulating lane
• C. 1 entry lane and 2 circulating lanes
• D. 3 entry lanes and 1 circulating lane

Answer: (A)

The configuration with one entry lane and one circulating lane is often noted for its inefficiency in performance when it comes to handling traffic flow at roundabouts. This design restricts the amount of traffic that can enter the roundabout simultaneously, leading to congestion. Since there is only one lane for entering traffic, vehicles must yield to all circulating traffic, which can create delays, especially during peak hours or times of heavy traffic.

Additionally, when the entry lane is limited to one, it can fail to accommodate added vehicles waiting to enter, causing backups that can extend into the adjacent roadways. This jams not only the roundabout itself but can also hinder traffic flowing onto the roundabout from nearby intersections.

On the other hand, configurations with multiple entry lanes generally improve performance because they allow more vehicles to enter the roundabout simultaneously, distributing traffic more effectively. This can lead to reductions in wait times and improved overall flow. Thus, having multiple lanes in both the entry and circulating sections usually results in better operational performance compared to a single lane in the entry point.