Civil Engineering Department, Sharif University of Technology, Tehran, Iran.
PLoS One. 2023 Feb 21;18(2):e0281951. doi: 10.1371/journal.pone.0281951. eCollection 2023.
The relationship between mean speed and crash likelihood is unclear in the literature. The contradictory findings can be attributed to the masking effects of the confounding variables in this association. Moreover, the unobserved heterogeneity has almost been criticized as a reason behind the current inconclusive results. This research provides an effort to develop a model that analyzes the mean speed-crash frequency relationship by crash severity and type. Also, the confounding and mediation effects of the environment, driver, and traffic-related attributes have been considered. To this end, the loop detector and crash data were aggregated daily for rural multilane highways of Tehran province, Iran, covering two years, 2020-2021. The partial least squares path modeling (PLS-PM) was employed for crash causal analysis along with the finite mixture partial least squares (FIMIX-PLS) segmentation to account for potential unobserved heterogeneity between observations. The mean speed was negatively and positively associated with the frequency of property damage-only (PDO) and severe accidents, respectively. Moreover, driver-related variables, including tailgating, distracted driving, and speeding, played key mediation roles in associating traffic and environmental factors with the crash risk. The higher the mean speed and the lower the traffic volume, the higher odds of distracted driving. Distracted driving was, in turn, associated with the higher vulnerable road users (VRU) accidents and single-vehicle accidents, triggering a higher frequency of severe accidents. Moreover, lower mean speed and higher traffic volume were positively correlated with the percentage of tailgating violations, which, in turn, predicted multi-vehicle accidents as the main predictor of PDO crash frequency. In conclusion, the mean speed effects on the crash risk are entirely different for each crash type through distinct crash mechanisms. Hence, the distinct distribution of crash types in different datasets might have led to current inconsistent results in the literature.
文献中平均速度与碰撞可能性之间的关系尚不清楚。这种矛盾的发现可以归因于该关联中混杂变量的掩盖效应。此外，未观察到的异质性几乎被批评为当前不确定结果的原因之一。本研究旨在通过事故严重程度和类型来开发一种分析平均速度-事故频率关系的模型。此外，还考虑了环境、驾驶员和交通相关属性的混杂和中介效应。为此，伊朗德黑兰省农村多车道公路的环形检测器和事故数据按日汇总，涵盖了 2020 年至 2021 年两年的时间。偏最小二乘路径模型（PLS-PM）用于事故因果分析，同时使用有限混合偏最小二乘（FIMIX-PLS）进行分段，以解释观测值之间潜在的未观察到的异质性。平均速度与仅财产损失（PDO）和严重事故的频率呈负相关和正相关。此外，驾驶员相关变量，包括追尾、分心驾驶和超速，在将交通和环境因素与事故风险联系起来方面发挥了关键的中介作用。平均速度越高，交通量越低，分心驾驶的可能性就越大。反过来，分心驾驶又与弱势道路使用者（VRU）事故和单车事故相关，从而导致严重事故的频率更高。此外，平均速度越低，交通量越高，与追尾违规的百分比呈正相关，而追尾违规又预测了多车事故，是 PDO 事故频率的主要预测因素。总之，平均速度对每种事故类型的碰撞风险的影响通过不同的碰撞机制而完全不同。因此，不同数据集中事故类型的不同分布可能导致了文献中当前不一致的结果。
