a School of Transportation , Southeast University , Nanjing , China.
Traffic Inj Prev. 2013;14(8):861-6. doi: 10.1080/15389588.2013.775433.
To evaluate the impacts of speed variation on the likelihood of traffic collision in various types of traffic states in a freeway section.
The overall traffic state is divided into free flow (FF), congested traffic (CT), back of queue (BQ), and front of queue (FQ) according to the speed at up- and downstream detector locations. Based on 448 crash recordings from a freeway stretch in California, the logistic regression model is used to estimate the impacts of average speed (AS) and standard deviation of speed (SD) as well as coefficient of speed variation (CSV) for each traffic state separately.
For the overall state, both the SD and CSV are significantly related to the traffic collisions. For the separate states, the model estimates vary in different states: in FF, the CSV is positively related to collisions, whereas the SD is not a good indicator for collisions; in CT and BQ, the SD and CSV have positive impacts on the collision likelihood (especially for rear-end collisions); in FQ, the speed variation indexes were not found to have significant impacts. The coefficients of SD and CSV were found to be different in distinct traffic states. The impact of AS was significant only in FF and BQ.
Considering the overall traffic as one state could hide important relationships between speed variation and collisions. The impacts of speed variation on collision likelihood are different in various traffic states. The SD and CSV are effective surrogate safety measures for traffic collisions in CT and BQ but may not be good measures in FF and FQ. The AS is an accident determinant in FF and BQ but not a contributing factor in other states.
评估速度变化对高速公路路段不同交通状态下发生交通碰撞可能性的影响。
根据上下游探测器位置的速度，将整体交通状态分为自由流（FF）、拥堵交通（CT）、队列尾部（BQ）和队列头部（FQ）。基于加利福尼亚州一段高速公路上的 448 次碰撞记录，使用逻辑回归模型分别估计平均速度（AS）、速度标准差（SD）和速度变化系数（CSV）对每个交通状态的影响。
对于整体状态，SD 和 CSV 都与交通碰撞显著相关。对于单独的状态，模型估计在不同状态下有所不同：在 FF 中，CSV 与碰撞呈正相关，而 SD 不是碰撞的良好指标；在 CT 和 BQ 中，SD 和 CSV 对碰撞可能性有积极影响（尤其是追尾碰撞）；在 FQ 中，速度变化指标没有发现显著影响。SD 和 CSV 的系数在不同的交通状态下有所不同。AS 的影响仅在 FF 和 BQ 中显著。
将整体交通视为一个状态可能会掩盖速度变化与碰撞之间的重要关系。速度变化对碰撞可能性的影响在不同的交通状态下是不同的。SD 和 CSV 是 CT 和 BQ 中交通碰撞的有效替代安全措施，但在 FF 和 FQ 中可能不是很好的措施。AS 是 FF 和 BQ 中事故的决定因素，但不是其他状态的促成因素。
