A simulation study on traffic conflict risk under shockwave propagation at signalized intersections

Traffic congestion and safety at signalized intersections are critical concerns in urban mobility management. The interaction between shockwaves caused by stop-and-go vehicles and the resultant conflict risk remains inadequately understood, necessitating detailed investigation. This study aims to explore the relationship between traffic conflict risk and shockwave propagation at signalized intersections through simulation, focusing on the dynamic conditions as vehicles queue and dissipate. The vehicle trajectory data extracted from the video captured by unmanned aerial vehicles (UAVs) is utilized in this study. The Simulation of Urban MObility (SUMO) software was selected as the simulation platform for building the simulation model. To ensure accuracy, the trajectories are refined with data smoothing and sampling, providing a reliable benchmark input for the simulation model development. Moreover, surrogate safety measures (SSMs) such as modified time to collision (MTTC) and deceleration rate to avoid a crash (DRAC), along with shockwave analysis (SA) were used to investigate the impact of driving risk when shockwave propagates in the queue. Then, the relationship between shockwaves and driving risk was explored under the calibrated model in a signalized intersection scenario. The study results show that conflicts occurred during the process of vehicles approaching until they stop and join the queue. Subsequently, the risk propagated at the tail of the growing queue. Additionally, the space-time diagram reveals that the risk propagation may be initiated before or along with the shockwave's propagation. The findings provide insights for developing control strategies at signalized intersections through the uncovered correlation between the conflict risk and shockwave, contributing to the comprehensive understanding of traffic flow and safety at intersections.