The proposals can be viewed here.
Perne Road is also the A1134 Ring Road. All of the Ring Road roundabouts are statistically bad for cyclists' safety and the council want to fix this. That is not in dispute.
The proposals involve moving cyclists onto shared use paths which cross the arms of the four junctions of the roundabout where they would have to give way crossing the arms of the roundabouts.
Just off the plans, the busier north and south arms of Perne Road already have pedestrian signalled crossings about 40 metres away from the centre of the roundabout. The online proposals do not mention upgrading these to Toucan so people on bikes can legally use them.
Cyclists would have to choose using the shared use pavement for safety, or remaining on the road. Shared use is popular with cyclists when uninterrupted, but disliked for the amount of give-ways and hold ups they introduce. Vulnerable pedestrians do not like to share pavements with cyclists, and is a source of constant complaining.
The Dutch have solved many of the issues of two-tier provision, with a three tier provision in busier locations, clearly separating pedestrians, cyclists and motor vehicles.
One of the arguments against three-tier provision in the UK and Cambridge is that it requires a lot of space, but that is not the case at this roundabout. Below I make a crude comparison of size with a roundabout from Groningen in Holland.
The following pictures are taken from Google Maps at similar zoom levels, rotated for easy comparison.
Google StreetView links:
Perne Road / Radegund Road, Cambridge.
Bakboordswal / Loefzijde, Groningen.
|Perne / Radegund Roads, Cambridge
|Bakboordswal, Groningen, Holland
|Both images combined. Similar sized roundabouts.
I will hold my hands up and say, I do not know if the Dutch roundabout works in practice. I believe the Groningen roundabout is is what cycling campaigners want. It is a subtle change from shared use but has very clear separation. A big question is will the road markings across junction arms work in a UK context on a Ring Road? See the view of a roundabout exit (note driving on right)
My reading of Dutch design is that filtering of traffic is a big part of what they do and cannot be captured from Google Maps. My gut feeling is that the Dutch route has far less traffic than the Cambridge Ring Road.
The two-tier proposed solution is commonly used in Cambridge and can be safer if you are prepared to stop at side roads and look very carefully but its inconvenient. I find myself unable to use safe facilities for cross city journeys - it just takes too long - and as a result I find myself switching to car or motorbike when I am not in the mood or don't have the legs for fast highly assertive riding required to keep me safe on direct routes.
I'd label shared-use with Safety through Inconvenience. If we could fit in a working Dutch roundabout we could have safety AND convenience. Solutions like this make more journeys viable by bike.
If Cambridge really wants to improve cyclist safety and traffic growth, it needs to be braver with its junction design.
Responses to the Perne Road roundabout proposals have also been made by Cambridge Cyclist and RadWagon.