Bicycle Network: Good Design Guides
Roundabouts - multi lane
How to reduce the negative effects of multi-lane roundabouts on a bike route.
3 June 2009. Fatalities and serious casualty accidents are likely to occur at busy multi lane roundabouts on bike routes. For these locations signalisation is likely to be the solution. See also single lane roundabouts.
The problems at the St George's Road roundabout illustrate some of the problems and possible solutions. Link to the story of the development of the bike route through this roundabout.
In a five year period 8 fatal bicycle motor vehicle collisions occured at this roundabout A Grogan Richards report said 'A closer investigation of the casualty accidents at the intersection indicates that all
accidents generally occur outside of the peak periods with the speed of southbound
vehicles contributes to the safety problem as they are not required to slow down to
travel through the roundabout.'
A study of vehicle speeds by John Piper Traffic on the roundabout at the times when the fatal collisions were most likely showed an average speed of 35kmh, an 85th percentile speed of 40kmh and top speeds up to 58kmh. The report said that the appropriate speed to enter the roundabout is around 20 - 30 kmh. This is not surprising as the roundabout offers little deflection - for southbound drivers moving down the page through the collision locations it is a gentle curve.
The signalisation design removes some of the vehicle movements and increases the deflection.