Debunking Stubborn Roundabout Myths

Posted By Les Conklin on Sep 30, 2017

By Jennifer Banks, Department of Transportation, City of Scottsdale

Northsight Roundabout. Courtesy City of Scottsdale.

Despite impressive safety numbers, shorter travel time and other benefits, roundabouts have been relatively slow to catch on. Scottsdale transportation officials believe this may be due to several myths surrounding roundabouts:

Myth: “Roundabouts,” “traffic circles” and “rotaries” are all essentially the same thing.

“When people hear ’roundabout,’ they sometimes think of the large, high-speed circular intersections more common in Europe and the eastern U.S.,” said Scottsdale Principal Traffic Engineer George Williams. “Those are rotaries, not modern roundabouts.”
Modern roundabouts must meet a minimum of three criteria:

1. All traffic must move counterclockwise around a raised, circular center median.
With rotaries, traffic is sometimes routed through the center or under the circle.

2. The roundabout must be designed to keep traffic speeds between 15 and 25 miles per hour.
Traffic speeds in the larger rotaries tend to be much faster, and neighborhood traffic circles meant for traffic calming often force very slow traffic speeds.

3. All entering traffic must yield to traffic already in the roundabout.
With rotaries, multiple types of entries are often used for one rotary, including stop-controlled, merge-controlled and yield-controlled. Traffic signals sometimes control both entering traffic and traffic already in the rotary.

Myth: Roundabouts have less capacity than other intersections.

Capacity at roundabouts is typically much greater than at signals, and the capacity of an all-way stop is half at best.

Myth: The primary purpose of roundabouts is to calm or slow traffic.

While roundabouts encourage cars to travel at speeds of 15 to 25 miles per hour, the purposes of roundabouts are to improve safety, traffic flow and capacity at an intersection.

Myth: Roundabouts increase drive times.

Because of their continuous flow, travel is faster with roundabouts.

“With roundabouts, all cars move slowly,” said Basha. “The go-stop-go of traffic signals and stop signs is much more time consuming.”
Myth: Roundabouts cost more to construct than signalized intersections.

While it costs more to construct a roundabout than a four-way stop, it costs about the same to construct a roundabout as it does a signalized intersection. Roundabouts tend to be cheaper over time as they do not require electricity or maintenance of signals.

Myth: Roundabouts require more space than signalized intersections.

While roundabouts require more space than a four-way stop, they take up about the same or often less space than a signalized intersection, particularly when left- or right-turn lanes are necessary.

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