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Delaware Department of Transportation

Delaware Roundabouts

Roundabout History

It all began around 1905...

Columbus CircleTraffic circles have been part of the transportation system in the United States since 1905, when the Columbus Circle designed by William Phelps Eno opened in New York City. After that, many large circles or rotaries were built in Canada and the United States. The designs at that time allowed vehicles to merge and weave at high speeds. Entering vehicles had the right-of-way, allowing high-speed entries. High crash experience and congestion in the circles led to rotaries falling out of favor in North America after the mid-1950s. Internationally, the experience with traffic circles was also bad, as many countries found that traffic circles locked up as traffic volumes increased.

Changes in the United Kingdom created the modern roundabout...

The modern roundabout was developed in the United Kingdom to fix traffic circle problems. In 1966, the United Kingdom adopted a mandatory "give-way" rule at all circular intersections that required entering traffic to give way, or yield, to circulating traffic. This rule prevented circular intersections from locking up, by not allowing vehicles to enter the intersection until there were enough gaps in circulating traffic. In addition, smaller circular intersections were proposed that made vehicles turn more tightly, resulting in slower entry and circulating speeds.

Modern roundabouts have improved traffic safety and traffic operations over older circles...

These changes improved the safety of the circular intersection by reducing the number and particularly the severity of collisions. The modern roundabout is significantly different from the older traffic circle both in how it operates and in how it is designed. The modern roundabout is greatly improved in terms of operations and safety, when compared with older rotaries and traffic circles. Many countries have adopted the modern roundabout as a common intersection form.

Modern roundabouts have improved environmental impacts...

A well designed, strategically placed modern roundabout is better for the environment than a signalized intersection because it creates shorter delays for motorists and shorter vehicle queues. The longer delays associated with traffic signals result in more vehicles idling for longer periods. Vehicles approaching a roundabout tend to arrive in a slow "rolling" pace rather than the typical stop/start behavior at signalized intersections. This results in lower fuel consumption. Recent studies have shown that idling vehicles emit larger amounts of some types of pollutants than vehicles traveling at moderate speeds. Based on this finding, fewer idling vehicles at a roundabout will result in lower emissions of certain pollutants than the same traffic at a signalized intersection.

References: Federal Highway Administration, Roundabouts: An Informational Guide, Report No. FHWA-RD-00-067, June 2000.

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