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Roundabouts

A roundabout is a circular intersection designed for improved traffic flow at a slower speed. Traffic circulates in a counter clockwise direction around a centre island. Vehicles entering the roundabout must yield to traffic already in the roundabout.

Benefits

Modern roundabouts help improve traffic flow and safety for motorists. Vehicles using a roundabout are not forced to stop, which reduces delays, congestion, noise, fuel consumption and emissions. Roundabouts also have lower operation and maintenance costs than traffic signals.

The safety benefits of roundabouts include:

  • traffic moves at slower speeds
  • fewer conflict points for pedestrians and motorists
  • reduced potential for right angle (t-bone) collisions
  • elimination of head-on and high speed collisions
  • more than 90% reduction in fatalities
  • 80% reduction in injuries
  • 40% reduction in total number of crashes

"Safety Effect of Roundabout Conversions in the United States: Empirical Bayes Observational Before-After Study." Transportation Research Record No. 1751, Transportation Research Board (TRB), National Academy of Sciences (NAS), Washington, D.C. 2001

Roundabout vs. Traffic Circles
Traffic circles have high-speed entries, allow lane changes within the circle, and have the potential for high-speed collisions. Sometimes motorists in the circle must yield to those entering. They have the effect of "free-for-all".

Roundabouts require motorist to yield on entry, don't allow lane changes, have reduced speeds, have high capacity and have fewer collisions.

Example of a traffic circle being converted to a mordern roundabout;

Modern Roundabout vs. Traffic Circle
Entering traffic yields to circulating traffic. Entering traffic merges or weaves into circulating traffic.
Circulating traffic doesn't stop. Circulating traffic comes to a stop when the circle fills with entering traffic.
Works well with heavy traffic. Breaks down with heavy traffic.
The deflection geometry and smaller circle requires traffic to slow before entering. The deflection geometry and larger circle allow traffic to enter at higher speeds.
Slower traffic promotes the yielding process. Higher speed traffic discourages the yielding process.
Slower traffic reduced serious collisions. Higher speed traffic increases serious collisions.

How to use a roundabout on Alberta’s highways

  1. Note the appropriate exit.
  2. As with any other intersection, choose the correct lane, before entering the roundabout.
  3. Slow down as you approach the roundabout, and be aware of crossing pedestrians.
  4. Yield to all traffic inside the circular lane, and wait for an appropriate gap.
  5. Maintain a safe speed, between 30 and 40 km/h, through the roundabout.
  6. Never change lanes within the roundabout.
  7. Signal for right turn as you approach the desired exit, while maintaining a safe speed.

For more information on driving through roundabouts, please visit the following page: http://www.transportation.alberta.ca/1993.htm.

Driving a Roundabout

* http://roundaboutresources.org

Truck Aprons
Roundabouts in Alberta have truck aprons around the centre island that provides extra room for semis and multiple-trailer trucks. The rear wheels of large trucks can drive across the truck apron, as they are designed to support the weight of large trucks and help long vehicles turn safely through roundabouts.

Typical Signs of a Roundabout

Information Sign

Indicates direction to destination

Regulatory Sign - Lane Control

Indicates lane choice prior to roundabout

Physical Conditions Sign

Indicates roundabout ahead

Other Roundabout Resources

http://roundaboutresources.org

http://safety.fhwa.dot.gov/intersection/roundabouts