Mediation pathways of contributing factors to left-turn safety at skewed intersections

Existing evidence suggests that geometric design, traffic control, environmental conditions, and driver behavior jointly affect left-turn safety at skewed intersections, while angle-specific influencing pathways remain poorly understood. This study conducted a paired driving simulator experiment with an L18 mixed-level orthogonal design covering intersection angle, left-turn lane offset, traffic control, lighting conditions, and pre-experiment safety briefing. Forty licensed drivers were recruited and generated 697 valid left-turn observations. CatBoost regression with permutation importance ranked key predictors, and angle-stratified path analysis decomposed variable direct and indirect effects. Average crossing speed and maximum deceleration were selected as mediating variables, with Post-Encroachment Time (PET) adopted as the surrogate safety indicator. According to the results, intersection angle and lane offset dominated variations in maximum deceleration and PET. At 60° intersections, zero and positive left-turn lane offsets and stop signs increased PET mediated by crossing speed. At 90° intersections, lane offset exerted the strongest direct effect, and guide lines raised speed and reduced PET with insignificant mediation. At 120° intersections, stop signs and guide lines improved PET via maximum deceleration mediation. The findings provide targeted angle-sensitive geometric and traffic control strategies for skewed intersection safety improvement.