Modified model of lane capacity at signalised intersections with waiting areas

Left-turn conflicts impact considerably the security and capacity of intersections. There are many practices to decrease conflicts and improve the efficiency of intersections, such as continuous flow intersection (CFI), contraflow left-turn lane, U-turn etc., however, the method of installing waiting areas (WAs) is common in China and it is easier to be accepted by Chinese drivers. Many studies have shown either theoretically or via simulation that WAs improve the traffic capacity greatly. However, few have considered how the vehicle start-up process and red clearance interval differ for lanes with and without WAs. Comparing the start-up lost time of intersections with and without WAs, This work explores the difference of clearance interval between intersections with and without WAs by conflict method, then establishes a modified capacity model about lanes with WAs. Finally, through field investigation of an intersection with left-turn WAs in Zhengzhou, the parameters needed for the modified model are determined. It is shown that the capacity of a lane with a 29-m WA and 18-s green time is increased by only 8.9%.