#34 Mini-roundabouts

Typically consisting of a painted circular road marking and sometimes a low traversable dome of small diameter, mini-roundabouts are a low-cost treatment to improve intersection safety. Mini-roundabouts are an option in low-speed environments where constraints such as limited space or cost may preclude the installation of a larger conventional roundabout or other controls such as traffic signals. According to Austroads and the US FHWA[1], early examples of mini-roundabouts date to the 1970s in the UK and France but have since been used in other countries, including Australia.

Effectiveness

Despite their small size and traversability, mini-roundabouts have demonstrated speed reduction and traffic calming effects, as well as modifying conflict angles to reduce collision severity. The FHWA reports general crash rate reductions of around 30% compared with signalised intersections. Citing a case study in Greater Melbourne on the installation of 43 mini-roundabouts, Austroads reported a 79% crash reduction, elimination of serious crashes, and increased speed limit compliance. A ‘network effect’ is noted, where multiple treatments along a route are expected to be more effective than a single isolated installation.

The low-speed environment should generally accommodate bicycles safely through mini-roundabouts. Pedestrian facilities such as raised crosswalks can also be included. Traversability allows access for larger vehicles and emergency vehicles, which may not otherwise be able to complete turns at a conventional roundabout of such small diameter.

[1] Federal Highway Administration (2010). Technical Summary: Mini-roundabouts. US Department of Transportation.