We are looking at a proposed development with a large roundabout (almost 25m radius central island). The large roundabout was proposed to mitigate offset entry roads but creates other geometric issues such as departure radii being less than desirable, etc. I believe that we can significantly improve these geometric issues & performance of the roundabout with an ellipse shaped roundabout. I however understand that the RMS do not support elliptical roundabouts (not sure why, driver expectation ??), however I have designed many elliptical roundabouts in the past with good outcomes.
Is anyone aware of any road safety issues associated with elliptical roundabouts that cannot be overcome with good design?
Good day Adam and all
There is a large elliptical multi-lane roundabout in Canberra, ACT, at the cross roads intersection of the Barton Highway with William Slim Drive and Gundaroo Drive, all with 80kph approaches. For many years it has been a major or principal ACT 'black spot'. The minor axis is the Barton Highway, which is not what you would expect. Obvious problems include big potential speed differentials between traffic along the major axis and the much slower minor axis route, exaggerated movements needed to remain in lane on minor axis entry, heavy vehicle roll-over risk, and recognising major axis right turners and through minor axis traffic, by traffic entering from the major route. It is a prime example of how to get a roundabout shape wrong. Currently, improvement efforts are being made by adding lanes and signal lights with the ACT Assembly opposition party going so far as to promise grade separation in lieu.
A look via Google maps will give an idea of the layout and difficulties.
The inference from this site is that a great deal of detailed consideration is necessary before deciding on the appropriateness of an ellipse roundabout solution.
Goodaye Adam, how much truck traffic will there be at this site? I have had numerous issues with round about design virtually contributing to truck rollovers. I spent much time dealing with TMR, but was never made awre it if bore any frouit or if better guidelines were put in place. Cheers Rod.
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