The Modern Roundabout

The modern roundabout is a circular intersection with specific design and traffic control features that separate it from other forms of circular intersections. A modern roundabout has major features compared to its predecessors, traffic circles and rotaries. Firstly, the modern roundabout is characterized by yield controlled entry points and channelized approaches. With the purpose of maintaining traffic flow, the circulatory roadway geometry ensures travel speeds are 50 km/h (30 mph) or lower (typically) and deflection angles that provide greater safety for motorists, cyclists, and pedestrians. Modern roundabouts are small, generally from 70 to 160 feet in diameter compared to 300 to 400 feet and more for traffic circles and rotaries. Modern roundabouts have a distinct feature of raised entry splitter islands which constrain vehicle speeds just before entry.

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benefits of roundabouts

Safer than signalized intersections

Intersection safety is a serious traffic problem in the United States. The Federal Highway Administration reports that, in just one recent year, approximately one death occurred every hour nationwide relating to intersections. Over nine thousand people lost their lives in traffic intersections in that recent year, equaling nearly one quarter of all traffic fatalities and amounting to a financial loss of over $96 billion.

Reduces frequency and severity of crashes

As speeds in modern roundabouts are often much slower than in intersections, any potential roundabout crashes are usually at lower speeds, and at less-dangerous angles (such as sideswipe). This translates into less severe injuries and property damage, if any. A study printed in the Transportation Research Record reported that converting 23 test intersections throughout the U.S. from traffic signals to roundabouts reduced injury crashes by 80 percent, and reduced all crashes by 40 percent, in those areas. Results were much the same for similar studies throughout the U.S. and Europe.

Reduces Traffic Delays / Increases Traffic Capacity

Traditional traffic signals usually stop two or more directions of traffic at one time. In roundabouts, all directions of traffic are often kept open and safely flowing. Several Insurance Institute for Highway Safety studies report significantly-improved traffic flow when traditional intersections are converted to roundabouts. A study of three such intersections in Nevada, Kansas and Maryland found that traffic delays were reduced 13-23 percent using roundabouts. Similar studies have shown a reduction of up to 89 percent in vehicle delays in roundabouts.

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Question: What is a roundabout?

Answer: A roundabout is an alternative form of intersection traffic control. A modern roundabout is a circular intersection with yield at entry. It promotes safe and efficient traffic flow. They were introduced in the U.K., but are gaining more widespread use in North America, with implementation in many U.S. states and several Canadian provinces. Typical characteristics of a modern roundabout include: Yield at Entry One-Way Travel around the central island (counterclockwise) Slower Speeds Roundabouts have the potential to reduce collisions, traffic delays and fuel consumption resulting in improved air quality through reduced vehicle emissions.


Question: What is the difference between a roundabout and a "traffic circle"?

Answer: Modern roundabouts are generally much smaller than older traffic circles, and require vehicles to negotiate a sharper curve to enter. These differences make travel speeds in roundabouts much slower than speeds in traffic circles. Because of the higher speeds in traffic circles, many were equipped with traffic signals or stop signs to help reduce potential collisions. In addition, some traffic circles operated according to the traditional yield-to-the-right rule, with circulating traffic yielding to entering traffic.


Question: How do roundabouts affect traffic flow?

Answer: Because approaching traffic only has to yield to vehicles already circulating in a roundabout, movement is often without delay. It has been shown that a roundabout can move traffic through an intersection at a much higher rate than traditional intersection controls.


how roundabouts work

Roundabouts do not use stop signs, but often use yield signs to notify each driver to first yield to approaching vehicles in the roundabout. Roundabouts are simple to use and, more importantly, safer than traditional intersections. Because navigating roundabouts is new to many North American residents, the following information will help steer you in the right direction.

  • As you approach, slow down and yield to pedestrians/bicyclists. For multi-lane roundabouts, choose the appropriate lane to use.
  • Yield to driver’s left. Those in the roundabout have the right-of-way.
  • Travel counter-clockwise through the roundabout.

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Useful links to videos are available below:

roundabouts database