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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. On normal roundabouts, the entry path radius should not exceed 100m, ensuring that the ‘deflection’ is sufficient to slow traffic to safe speeds.

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.

Roundabouts are beneficial to assist drivers adapting to a change in road types, mark the start of bypass and serve as a gateway to urban areas.

Continental European (compact) roundabouts with a tighter geometry and often a single lane layout have good safety performance.

More sophisticated design such as turbo roundabouts can have significant merits in terms of road safety and capacity.

Signalisation of large and busy roundabouts can have significant merits in terms of road safety and capacity.

However, roundabouts can create barriers for pedestrians and pose safety risk for both bicyclists and pedestrians. Therefore, roundabouts should be used cautiously on roads used by bicyclists and with high pedestrian volumes.

The Star Rating Demonstrator is a freely available tool with the iRAP online software, ViDA. With the Star Rating Demonstrator, it is possible to explore the impact that this Safer Roads Treatment has on risk.

Treatment Summary


Medium to high

Treatment life

10 years - 20 years

Potential casualty reduction

60% or more

Case Studies

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