Traffic safety risk assessment and characterization of lane-changing behavior in urban expressway interchange weaving area

• The study covers the full lane-changing process, from the car-following phase to the execution of the maneuver itself. • The conflict rate changes with the position of the vehicle's lane change starting point in the weaving area. • A comprehensive safety risk assessment method for the entire lane-changing process was proposed. • Vehicles with certain driving behaviors are more likely to have higher risks, such as continuous or short lane change. The urban expressway interchange (UEI) weaving area is a special weaving section type and has a complex safety environment. The purpose of this study is to assess the traffic safety risk and analysis characteristics of lane-changing behavior in the UEI weaving area. Traffic safety risk is divided into instantaneous risk and overall risk. Risk characteristic indexes of rear-end and sideswipe conflicts are constructed and the K-means method is applied to assess the instantaneous risk. To assess the overall risk, the integrated risk index considering the distribution of instantaneous risk along the lane-changing process is calculated by faulty tree analysis. Then the field collected lane-changing trajectory data in the UEI weaving area is applied to the proposed risk assessment method and characteristics analysis is conducted. The results show that sideswipe conflict occurs more frequently in terms of conflict types, and lane-changing vehicles are more likely to have conflicts with the vehicles ahead, including those in the current lane and the target lane. Lane-changing behaviors with short lane-changing distance or crossing at least two lanes are among the main contributing factors for high overall safety risk. In general, the safety situation of the UEI weaving area needs to be improved. The proposed method may be applied to lane-changing decision making in assisted driving, and characteristics analysis results could be used to optimize the organization scheme in the UEI weaving area.