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. (a).

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