Flying Dodo
It'll soon be summer
Not wishing to appear cynical, but what evidence is there that traffic will slow down for a turbo roundabout? Since this is the fist one in the UK I guess there is no precedent but they are used in the Netherlands - do they slow down cars there?
From the reports I have seen a turbo roundabout increases vehicular capacity. This doesn't necessarily mean an increase in speed but it definitely means an increase in traffic flow which I would have thought might make it more difficult to move to the right lane on the approach.
As far as I was aware a turbo roundabout was a sort of semi slip road concept where, because the lanes were more segregated motorists taking a first (or second?) turnoff would be able to progress more quickly onto the roundabout even if there was traffic already on it but going round to another exit. None of this seems to me to indicate that a turbo roundabout would be kind to cyclists.
The actual designer of the junction, Patrick Lingwood, who is the Walking & Cycling Officer at Bedford Borough Council explains the details here.
based on the radius of curvature of vehicular paths, ..... this will reduce motorised vehicle speeds from current 25mph to around 10-15mph, approximating much more to cycling speeds.
A detailed analysis of the accidents suggests a 75% reduction in serious accidents and 40% reduction in slight accidents for all modes, including cyclists.
As I've already stated, sadly it won't help off road cyclists partly because there's no space to put in fully segregated cycle paths all the way round. It's also due to the fact that toucan crossings are the only crossings that traffic will stop for. Here in the UK we haven't got anything like a zebra crossing for cyclists.