Quite often there isn’t room for a Dutch-style roundabout. The Swiss have experimented with the geometry of roundabouts to make them as cycle-friendly as possible, with cyclists still on-road. This is unlikely to be comfortable enough for family cycling, so alternative quiet routes will also be needed that avoid the area.
The roundabouts need to be big enough so the entries can be tight, but not so big that cars try to overtake bikes on the roundabout. The diameter of the roundabout should be 24-34m, and the circulating carriageway should be no-more-than 8m wide. The Swiss advice is that exits should be quite open, to avoid the risk of cyclists getting cut up on exit. The design can cope with quite high traffic levels – upto 30,000 motor-vehicles per day, according to the Swiss.
This is a sketch design for a pair of mini-roundabouts in Marston, Oxford. The give-way lines have been moved back to make a bigger roundabout with a solid island, and the number of approach lanes reduced to one on each arm. Cycle lanes have been added on all the approaches. The road between the two roundabouts has been narrowed and angled, to slow the traffic.
The original aerial imagery is from Google Maps.