Double-lane roundabout capacity

Exhibit 4-4 shows the expected capacity of a double-lane roundabout that is based on the design templates for the urban/rural double-lane roundabouts. The capacity forecast shown in the chart is valid for double-lane roundabouts with inscribed circle diameters of 40 m to 60 m (130 ft to 200 ft). The capacity forecast is based on simplified British regression relationships, which may also be derived with a gap-acceptance model by incorporating limited priority behavior. Larger inscribed diameter roundabouts are expected to have slightly higher capacities at moderate to high circulating flows.