集计与非集计速度一致性指标的差异性及应用

Aggregateand Disaggregate Speed Consistency Metrics:Differences and Application

速度差及速度离散性对道路交通安全有重要影响,均可作为速度一致性指标,用于交通安全评价.将速度一致性指标分为集计与非集计两类,从数理上解析传统集计性指标(以运行速度为代表)的两个主要缺陷,即生态学谬论与过高估计安全性.在建立交通安全水平分级标准的基础上,利用运行速度差△V_(85)、85位单车速度差85(△V)和85位单车速度变化率85(△V)R对沪宁高速南京段37个高速公路出口进行了对比性安全评价.结果表明,单车速度变化率可以考虑上游路段初始速度;非集计速度指标可有效避免生态学谬论及过高估计安全性的缺陷.

Speed difference and discreteness, which closely related to traffic safety, can be introduced as metrics of speed consistency to assess safety performance. The speed consistency metrics are classified into two categories, namely, the aggregate and disaggregate ones. The two main shortcomings of the aggregate metrics, ecological fallacy and safety overestimation, are deduced and verified by mathematic analysis. Based on the given safety evaluation criterion, the safety levels of 37 exits along freeway G42 in Nanjing, China, are appraised using the conventional aggregate measure, operating speed AVs5 , the 85 th percentile individual speed difference 85 （AV） , and the 85 th percentile individual speed change rate 85 （Av）R. The comparative analysis indicates that the disaggregate speed consistency metrics are capable of avoiding the pitfalls possessed by aggregate metrics to a certain extent. Thus, the disaggregate speed metrics should be adopted in road safety evaluation in both the fields of research and engineering application.