Capacity measurements on experimental roundabout designs at Swindon.

In an experiment at the 5-arm county island roundabout in Swindon, the capacity of the original roundabout was compared with that of various experimental roundabout layout within the same outline of 75 x 85 m. A reduction of the central island from an oblong 60 x 75 m to a circle of 38 m diameter increased the capacity by about 33%. A change to a ring junction, i.e. two-way circulation with a mini-roundabout at the mouth of each of the five roads, increased the capacity by 20% over that of the original. The operation of the various lay outs tested is discussed.