Intersection - Roundabout

A roundabout is a one-way roadway around a circular central island. Entry to roundabouts is controlled by 'give-way' markings and signs. Vehicles already on the roundabout typically have right-of way.

Roundabouts cause little delay in low to medium traffic flows, and require less maintenance than signalized intersections.

Geometric design is crucial to the safety of a roundabout. Curves on the approaches to require all vehicles to slow down before entering. The centre island layout ensures that traffic moves in a one-way direction and that slow speeds are maintained around and at exits to the roundabout.

The rules governing roundabout use also help to improve safety. Drivers approaching a roundabout need to slow and give way to vehicles already in the roundabout, and be prepared to stop.

As a result, roundabouts can virtually eliminate often severe right-angle, left-turn (or right-turn), and head-on collisions.

  • Minimal delays at lower traffic volumes.
  • Little maintenance required.
  • Crash severity is usually lower than at cross intersections.
  • Solid structures should not be located on the central island.
  • High painted kerbs around the island can reduce the risk of it being run into.
  • Poor visibility on the approach to roundabouts, or high entry speeds, can lead to crashes.
  • Facilities to help pedestrians cross the arms of the intersection should be provided in most urban locations.
  • Roundabouts can be difficult for large vehicles, particularly buses, to use.
  • Designers should be conscious of the risk that roundabouts can be present for cyclists and other slow vehicles, such as animal drawn vehicles.

Benefits

  • Minimal delays at lower traffic volumes.
  • Little maintenance required.
  • Crash severity is usually lower than at cross intersections.

Implementation issues

  • Solid structures should not be located on the central island.
  • High painted kerbs around the island can reduce the risk of it being run into.
  • Poor visibility on the approach to roundabouts, or high entry speeds, can lead to crashes.
  • Facilities to help pedestrians cross the arms of the intersection should be provided in most urban locations.
  • Roundabouts can be difficult for large vehicles, particularly buses, to use.
  • Designers should be conscious of the risk that roundabouts can be present for cyclists and other slow vehicles, such as animal drawn vehicles.

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