Safety evaluation of freeway basic segment based on CPMs and LOSS

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Xiang-hai Meng
Wei Qin
Xin Li

Safety evaluation of basic segments of freeway plays an important role in freeway safety management. Common methods for dividing basic segments were introduced and compared at first, and then a dynamic cluster segment division method was put forward based on where crashes located. Based on the numbers of crashes on divided segments, the statistical distribution of crashes was analyzed, and the result showed that the number of crashes on the divided segments followed the Negative Binomial (i.e., NB) distribution. Hence, Crash Prediction Models (i.e., CPMs) based on the NB distribution were established, and a method to evaluate the safety situation of freeway was proposed. Furthermore level of service of safety (i.e., LOSS) was introduced and the classification standard was determined, then a segment safety evaluation method based on LOSS was put forward. Both methods based on CPMs and based on LOSS were applied to the Jingzhu freeway, and the comparison showed that 57.8% segments were under the same level while the other were different. What’s more, it also could be find that the evaluation result based on CPM methods is more in line with actual situation. Safety evaluation method based on NB distribution considers traffic volume and geometric alignment, so it is more suitable for the freeway with complex geometric alignment conditions, mountainous freeway as Jingzhu freeway for instance. On the other hand, the safety evaluation method based on LOSS considers traffic volume and crash number, so it is more suitable for the freeway with good geometric alignment conditions.

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