Entry capacity loss at multilane roundabouts caused by rainfall was investigated. Traffic and rainfall data were collected continuously for eight weeks at selected sites in South Africa and Malaysia. ree classes of rainfall (light, moderate, and heavy) were used. Both linear and exponential techniques were used to model the relationship between entry and circulating traffic flows. Correction factor for entry angle and radius was introduced in the linear model equations to allow for variations in geometric data. Correction factor is not required for the exponential model technique. Notwithstanding, both techniques predicted that entry capacity loss would result from rainfalls irrespective of their intensity. Results show that light rainfall may cause about 5% entry and circulating capacity loss, moderate rainfall may cause about 12% capacity loss, and heavy rainfall may cause about 17% capacity loss. is paper proposed further studies into the effect of two circulating lanes rather than one on entry capacity at roundabouts.

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.

Background: This paper filled an important gap in the behaviour of driver and gap acceptance model at multilane roundabouts by investigating their traffic performances during rainfall. Introduction: The study carried out an investigation into the impact of rainfall on driver’s behavioural changes and gap acceptance characteristics. Follow-up time headway and gap time were used as proxies. Methodology: Traffic volume, speed, vehicle type and headway data were collected at selected multilane roundabouts in Durban, South Africa. All surveyed roundabouts are within rain gauge catchment area of about 1km. Rainfall intensity was divided into three groups (light, moderate, and heavy). Dry weather data were used as control parameters. Data Analysis: Stepwise data analytical technique was used for ease of explanation and clarity. All model equations were tested for statistical fitness and deemed satisfactory for further analysis. Conclusion: Based on the synthesis of evidence obtained from driver’s behavioural changes and gap acceptance characteristics at multilane roundabouts, the paper concluded that it is correct to suggest that rainfall would have a profound effect on follow-up time headway and critical gap acceptance. However, the effect diminishes gradually as volume to capacity ratio approaches peak traffic operation. Once the threshold value of 0.85 is reached the diminishing effect of rainfall as the sole actuator of anomalous time headway increase is noticeable.

The paper investigated the extent to which rainfall influences the quality of service delivery at multilane roundabouts using a novel quality of service approach. Quality of service is defined as how well roundabouts operate based on road users and road providers’ perception of service quality. Delay and reserve capacity were used respectively as proxies for road users and road providers’ perception of service quality. The entry and circulating traffic data were recorded continuously for eight weeks under dry, light, moderate, and heavy rainfall weather conditions at each surveyed roundabout, then collated, analysed and compared. Linear regression with dummy variable was used to model the roundabout entry capacity and a corrector factor was added to modify the regression function. The corrector factor considered different entry radii and entry angles of surveyed roundabouts. Multi-criteria quality of service table with travel time as proxy for road users and speed as proxy for road providers’ perception of service delivery was developed from peak traffic data and used to determine the extent of deterioration. The multi-criteria table introduced in the paper is a clear departure from the speed-based criteria used in many studies. The results show a significant increase in time delay and a decrease in reserve capacity relative to rainfall. The paper has concluded that rainfall has an anomalous negative effect on the quality of service at multilane roundabouts. The findings could be used in a variety of ways in traffic management to predict the travel time at roundabouts under rainy conditions and to prescribe speed limits accordingly.