The Capacity of Some Grade-Separated Roundabout Entries

摘要

The report describes measurements of the entry capacities of seven grade-separated roundabout entries fed by motorway exits. The objective of the study was to compare the entry capacities of these entries with those predicted by a 'unified' formula developed recently for at-grade roundabouts and so to develop a capacity prediction method for grade-separated roundabouts. The entry capacities of the grade-separated roundabouts at the mean value of circulating flow did not differ significantly from the predictions of the unified formula. The entry/circulating flow relationship, however, were found to have steeper slopes than those appropriate to at-grade roundabouts. A modification to the 'unified formula' for the entry capacity of at-grade roundabouts has accordingly been derived so as to provide a method for predicting the capacities of grade-separated roundabouts. The effects of traffic engineering measures taken to improve the capacities of four of the entries were also studied.