The report describes an experiment carried out at a four-arm roundabout at Colchester in which the capacity of the original design was compared with the capacities obtained with two new designs. The new layouts were a small-island roundabout and a ring-junction. The latter consist of a ring of four mini-roundabouts and was designed to make passage through the junction easier for right- turning traffic. During the course of the experiment three versions of this design were installed. The carriageway outline, with an inscribed-circle diameter of 60 m, was the same in all the layouts. The small island roundabout, where the diameter of the central island had been reduced from the original 36 m to 20 m, increased the capacity by about 12 per cent and the final ring junction design increased the capacity by a further 5 per cent. Some measurements of delay to traffic are reported. The operation of the new junction designs are discussed. (Author/publisher)
Abstract