A high proportion of road traffic crashes occur at intersections. Roundabouts are a primary safe system treatment commonly used to minimise the likelihood and severity of intersection crashes. Roundabout geometric design (including curves) causes drivers to slow on approach to the intersection, reduces the number of conflict points, and lessens the severity of impact angles. Roundabout safety performance is supported by appropriate signs and guidance on approach, sometimes including traffic signals.
While there are many variations in roundabout design and implementation, research shows reductions of up to 80% in the incidence of fatal and serious injury crashes[1]. Overall, these can be relatively low-cost treatments that improve efficiency in traffic movement. Vulnerable road users including pedestrians, cyclists and motorcyclists require specific consideration when selecting and designing optimal roundabout treatments.
Single-lane roundabouts
Single-lane roundabouts have the highest safety performance and are commonly found in urban areas, potentially replacing traffic signals, two-way and all-way stop controls. They may also be used to manage transition from high-speed to low-speed environments, such as at freeway off-ramps. Pedestrians may be safely accommodated with zebra crossings and/or raised platforms set back from roundabout entry points.
Multi-lane roundabouts
Multi-lane roundabouts are more complex than their single-lane counterparts. While still demonstrably effective for reducing crash rates and crash severity, the greater complexity leads to higher crash rates for multiple versus single-lane roundabouts. Research shows that rules for navigating roundabouts are sometimes poorly understood, and this may apply to both multi- and singe-lane roundabouts.
Signalised roundabouts
In some cases, roundabout safety performance can be improved through partial or full signalisation (i.e., applied to one or more approaches). This may be appropriate where continuous flows on one or more approaches prevent traffic entering from other approaches. Signals may also be used at roundabouts to give priority to vulnerable road users and/or public transport (e.g., buses).
[1] Information sourced from Austroads Guide to Road Safety Part 2 and (US) FHWA “Intersection Safety”.