Anomalous capacity shrinkage at multi-lane roundabouts due to rainfall

The purpose of the study reported in this paper was to investigate the extent of anomalous entry, circulating and reserve capacity shrinkage at multi-lane roundabouts due to rainfall. Traffic flows, vehicle speeds, vehicle types and rainfall data were collected, collated and analysed. Three classes of rainfall intensity (light, moderate and heavy) were considered. Linear regression analysis was performed in which entry traffic flow was considered a function of circulating traffic flow. A correction factor was used to account for different entry angles and entry radii. Exponential regression and the model proposed in the 2010 Highway Capacity Manual were used to check the linear regression outcomes. The results showed that rainfall caused anomalous entry and circulating capacity shrinkage by 5%, 12% and 17% due to light, moderate and heavy rain, respectively, and also showed that such rainfalls would cause reserve capacity shrinkage by 3·7%, 8·5% and 12·5%, respectively. It was concluded that rainfall causes anomalous capacity shrinkage irrespective of its intensity.