Channelized spiral roundabouts with all the permitted movements and the adaptation of the signage

Illustrations © Author

The increase in traffic volume coupled with the general poor use of multi-lane roundabouts is causing the demise of this type of road junction. This is due to drivers' refusal to use the inside lanes as they are harder to access and more dangerous to exit. As a result, they drive around the outside of the roundabout preventing others from exiting from the inside lanes or accessing the roundabout from the various entry points. The multi-lane roundabout therefore becomes congested, turning into a single-lane roundabout with a lower capacity. Turbo roundabouts are a good alternative as they have a greater capacity and fewer points of conflict. However, the signage is more complex and some movements are limited, such as reversals of direction or access from a secondary road towards another located behind the second channel (on two-lane turbo roundabouts).