Modelling U-Turning Behaviour of Vehicles at Mid-Block Median Openings in Multilane Urban Roads

Gap acceptance and lateral placing of vehicles are considered as prime parameters for analysing the behaviour of U-turning in vehicles at un-signalized median opening in urban areas. Critical gap is the sole parameter in gap acceptance phenomenon where critical position gives the vehicle’s location during U-turn operation. Data for this study were collected using video photography at six median openings on a sixlane road and three median openings on a four-lane road from two different cities of India. Data as extracted by categorizing the traffic stream into five different classes such as two-wheelers, three-wheelers, car/SUVs, LCVs (light commercial vehicles) and HCVs (heavy commercial vehicles). Three different methodologies (namely the traditional method, INAFOGA and modified Raff’s method) were utilized to estimate the critical gap. Critical position of vehicles is estimated using the markings on the pavement surface. Regression technique was used for modelling critical gap and position using different variables for each motorized mode. All the proposed models have a high coefficient of determination value which indicates its high significance level. Modelling of critical position for 3-wheelers was not framed as the P-value for each variable was higher than 0.05. The reason could be the randomness in data because of the undisciplined lateral movement of three-wheelers. A design recommendation for right turn pocket lanes near the median opening area is proposed especially for U-turning traffic based on the percentage of the U-turning traffic and maximum critical position of vehicles from the median edge.