Assessing the safety criticality of driver behavior toward cyclists at intersections

Objective: Detailed analyses of car-to-cyclist accidents show that drivers intending to turn right at T-junctions collide more often with cyclists crossing from the right side on the bicycle lane than drivers intending to turn left. This fact has led to numerous studies examining the behavior of drivers turning left and right. However, the most essential question still has not been sufficiently answered: is the behavior of drivers intending to turn right generally more safety critical than the behavior of those intending to turn left? The purpose of this article is to provide a method that allows to determine whether a driver’s behavior toward cyclists can retrospectively be assessed as critical or non-critical. Methods: Several theoretical considerations enriched by findings of experimental studies were employed to devise a multi-measure method. This method was applied to a dataset containing real-world approaching behavior of 48 drivers turning right and left at four T-junctions with different sight obstructions. For each driver a behavior-specific criticality was defined based on both, their driving and gaze behavior. Moreover, based on the behavior-specific criticality of each driver, the required field of view to see a cyclist from the right was defined and was set into relation with the available field of view of the T-junction. Results: The results show that only a small portion of the drivers within the dataset would have posed an actual risk to cyclists crossing from the right side. Those situations with a higher safety criticality did not only arise when drivers intended to turn right, but also left. Conclusion: Therefore, the analysis can only provide an explanation for the higher proportion of accidents between drivers turning right and cyclists crossing from the right side in certain situations. Further research, for example analyses of exposure data regarding the frequency of turning manoeuvers at T-junctions, is needed in order to explain the higher proportion of accidents between drivers turning right and cyclists crossing from the right side.研究目标：针对汽车与骑行者碰撞事故的详细分析显示，在T字路口（T-junction）右转的驾驶员，与在自行车道上从右侧横穿的骑行者发生碰撞的概率，高于左转的驾驶员。这一现象促使诸多研究针对左转与右转驾驶员的行为展开探讨。然而，最核心的问题仍未得到充分解答：右转驾驶员的行为是否普遍比左转驾驶员更具安全风险性？本文旨在提出一种方法，可回溯性地判定驾驶员针对骑行者的行为属于安全关键性或非关键性。 研究方法：本文结合多项理论考量与实验研究结果，设计出一套多指标评估方法。该方法被应用于一组真实世界数据集，该数据集包含48名驾驶员在4个存在不同视线遮挡的T字路口的右转与左转趋近行为数据。针对每位驾驶员，本文基于其驾驶行为与注视行为（gaze behavior），定义了行为特异性安全关键性指标。此外，基于每位驾驶员的行为特异性安全关键性，本文界定了观察右侧横穿骑行者所需的视野范围，并将其与T字路口的可用视野范围进行关联分析。 研究结果：数据集内仅少数驾驶员会对右侧横穿的骑行者构成实际风险。安全风险性较高的场景不仅出现在右转情境中，左转情境下同样存在。 研究结论：因此，本分析仅能解释特定情境下右转驾驶员与右侧横穿骑行者碰撞事故占比更高的现象。为进一步解释该类事故的高发比例，还需开展进一步研究，例如针对T字路口转弯操作频次的暴露数据（exposure data）分析。