Roundabouts: reducing traffic frustration

By: Drivers.com staff
Date: 2000-08-07

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Visitors to Britain since the 1950s nearly always mention roundabouts as the most noticeable feature of that country's highways system. If they're drivers, their reaction is usually one of initial confusion, until they realize who has the right of way, followed by admiration as to how well the system actually works.

Now North American engineers, impressed by the efficiency and safety of modern roundabouts, are at last following suit. British Columbia has had some in place for a decade, and roundabouts have recently been built in California, Colorado, Florida, Maryland, Nevada, and Vermont. Many more are on the drawing boards.

According to the Turner-Fairbank Highway Research Center (TFHRC), the era of modern roundabouts began in the United Kingdom in 1956 with the construction of the first "yield-at-entry" roundabouts. In 1966, a nationwide yield-at-entry rule launched the modern roundabout revolution. Australia and most other British-influenced countries soon built modern roundabouts.

The research center, which is the home of the Federal Highway Administration's (FHWA's) Research, Development, and Technology Service Business Unit, has just published a highly informative booklet entitled " Roundabouts: An Informational Guide ." The booklet can be downloaded free from the center's web site , or view the summary version in PDF .

The center admits that countries such as the United States, where people drive on the right side of the road, have been slower to follow Britain's example, but are rapidly catching up. For example, roundabouts have greatly increased in number in France since the adoption of the yield-at-entry rule on national routes in 1983.

Okemos roundabout in Ingham County, Michigan, USA.
Photo taken by the Ingham County Road Commission.

"Yield-at-entry is the most important operational element of a modern roundabout," says the center, "but it is not the only one. Deflection of the vehicle path and entry flare are also important characteristics that distinguish the modern roundabout from the nonconforming traffic circle, which does not have these characteristics.

"Other features include splitter islands at all approaches (to control entry speed and deter left turns), good sight distance, good lighting, good signing, no crosswalks across the circulatory roadway, yield lines downstream of the pedestrian crossings, and no parking in the roundabout."

Why are roundabouts safer?

"The physical configuration of a modern roundabout, with a deflected entry and yield-at-entry, forces a driver to reduce speed during the approach, entry, and movement within the roundabout," the center says.

"This is contrary to an intersection where many drivers are encouraged by a green or yellow light to accelerate to get across the intersection quickly and to 'beat the red light' and contrary to old traffic circles where tangent approaches also encourage, or at least allow, high-speed entries."

Another important safety factor is that the only movement at an entry and an exit of a roundabout is a right turn, thus reducing the potential frequency and severity of accidents compared to accidents typically occurring during left turns and when traffic crosses an intersection in perpendicular directions.

It is thought that one-way circular intersections were invented by a French architect, Eugene Henard, in 1877. During the same period, the American architect William Eno was also proposing his plan for small circles to alleviate traffic congestion in New York City. Since the adoption of a yield-at-entry regulation in 1966 by Great Britain and in1983 by France, there has been overwhelming interest and research in roundabouts because of the simplicity of their design and operation and particularly because of their safety.

"Enthusiasm for the safety and high capacity of roundabouts has resulted in a huge increase in the number of roundabouts," the center adds. "By contrast, as growing traffic demand causes nonconforming traffic circles to fail, they are converted to other types of intersections."

In modern times, the Netherlands has experienced spectacular growth of roundabouts beginning in the late 1980s. In only six years, approximately 400 roundabouts were built. The reasons given are: a drastic reduction in serious crashes; lower driving speeds; improved pedestrian crossing facilities; elimination of traffic signals, and high capacity with more than 2,000 motor vehicles and several hundred bicycles and mopeds per hour in one-lane roundabouts.

TFHRC says the first modern roundabouts in the USA were built in the spring of 1990 in Summerlin, a rapidly growing planned community on the west side of Las Vegas. With rapid growth of the surrounding community, daily traffic has increased from very low flows to about 7,000 vehicles in the north roundabout and to about 11,000 vehicles in the south roundabout. Only four accidents have been reported at the two roundabouts over their five-year history.

The first modern roundabout on the California state highway system was installed by the city of Santa Barbara in 1992. The roundabout replaced an intersection of five two-lane streets regulated by stop signs. The old intersection averaged four accidents per year. Since installation of the roundabout, accidents have averaged 2.1 per year, with only five accidents reported in a 28-month period.

Photo courtesy Peter Partington

One U.S. traffic engineer comes out resoundingly in favor of roundabouts over traffic lights. In a booklet prepared for the 1996 Roundabout Design Workshop in Montpelier, Vermont, Michael J. Wallwork says that for many years traffic signals have been seen by traffic engineers, officials, and the public as a panacea for traffic and crash problems at intersections.

"Often the traffic signals fail to meet expectations. They lengthen delays, the severity of collisions is likely to worsen, congestion and overall driver frustration increases with the proliferation of stopping points," says Wallwork.

"Traffic signals are ugly. They consume significant quantities of electricity, require costly maintenance, and often require traffic engineers to spend many hours in court, as attorneys for the plaintiff argue that traffic signals rather than any driver dereliction caused a crash.

"In their search for a better method to control conflicts at intersections, some progressive traffic engineers are now using modern roundabouts. The reason is that modern roundabouts are safer, cheaper, more efficient, have a higher capacity, and can be very attractive-especially as a gateway to cities and communities.

"I predict that engineers will increasingly realize that traffic signals are not the cure-alls that they have been promoted to be," Wallwork says." Roundabouts will be used in residential streets to reduce speeds and crashes, and on arterial roads to reduce crashes and provide a higher capacity. In all instances they are more cost effective and aesthetically pleasing, leading to public acceptance first, and public preference in the foreseeable future."

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