Analysis on Actual Capacity of Long Tunnel by Using Greenshields Model

Using Metro Count 5600, the speed and headway data of vehicles are collected at different sections of No. 3 Qing ling Tunnel, e.g. at the entrance, inside and at the exit. Based on the real surveyed data, the most commonly used linear expression model, Greenshields, is taken to fit them. According to the fitted curve, we obtain the change patterns of the three fundamental characteristics of traffic flow. The results show that the instantaneous speed is generally lower than 80 km/h at the entrance. As the drivers adapt to the tunnel environment, the speed becomes higher inside the tunnels. At the exits, most of vehicles accelerate. Our analysis of the headway indicates that the capacity inside the tunnel is lower than that of the entrances or the exits, which should be caused by the closed environment there. Therefore, for a whole tunnel, the capacity inside is used as the recommended value as the tunnel´s capacity. We conclude this paper by recommending different capacity values at each section for the further research.