An Analysis and Adjustment of the Abrupt Change of Vehicle Trajectories in the Entrance area of Freeway Tunnels

Vehicle trajectories would undergo abrupt changes at the entrance area of freeway tunnels. To analyze the reasons behind this phenomenon and quantitatively evaluate the regulating effect of different visual guiding schemes, four simulation scenarios are developed. Scenario 1, based on the guidelines outlined in Specifications for Design of Highway Tunnels Section 2 Traffic Engineering and Affiliated Facilities (JTG D70/2—2014), serves as the control group, while other scenarios incorporate visual guiding schemes on the basis of Scenario 1. Specifically, Scenario 2 introduces a low-position scheme consisting of flexible posts and crash cushions, Scenario 3 introduces a high-position scheme comprising retroreflective arches and warning alignment signs, and Scenario 4 combines both the low and high schemes. Through a simulated driving platform, data such as driving distance, steering wheel angle, and lateral offset are obtained, and an evaluation index system is established considering the occurrence, evolution, and fading of the abrupt change trajectories. The study results indicate that changes of the visual reference system can prompt abrupt changes of driving trajectories, but a continuous and consistent visual guiding scheme can regulate this phenomenon. Specifically, compared to the control group, the low-position scheme significantly reduced the average steering wheel angle before the tunnel entrance (SWAav) by 82%, helping drivers avoid abrupt maneuvers. High-position scheme increased the gradient coefficient (G) by 3.7 times, reduced the expected lateral deviation during the transient stability phase (O1) by 31%, and decreased the difference between O1 and the expected lateral deviation during the stable phase (O1－O2) by 75%. This improved the gradual change in trajectory, reduced avoidance of the tunnel portal and wall, and enhanced adaptation to the tunnel environment. The combined guiding scheme, which integrates both low and high-position scheme, yielded the best results: it increased G by 4.4 times, reduced SWAav by 83%, decreased O1 by 41%, and minimized O1－O2 by 98%. This scheme effectively improved the gradual nature of trajectory changes, reduced avoidance of the tunnel entrance and walls, and enhanced environmental adaptation. Consequently, it is recommended to implement the combined scheme in the entrance areas of highway tunnels, with the exception of special cases where only the high scheme should be applied.