基于自然间断点法的城市公交运行状况评价

Bus Operation Status Evaluation Based on Natural Breaks

摘要:

为克服城市异质性对公交运行状况评价结果稳定性的影响，采用自然间断点法对公交行程速度顺序统计量进行聚类，获取状态临界速度；以方差拟合优度及其增量为判据，确定状态最佳分类数；以临界速度绝对值、百分位数、与理想运送速度比值作为状态分类参数，评价其稳定性。结果发现：公交运行状态分为4类最佳，对应拥堵、缓行、畅行与自由流状态，存在拥堵速度、畅行速度与理想运送速度3个临界速度；临界速度与理想运送速度比值具有良好稳定性；拥堵速度、畅行速度与理想运送速度比值分别稳定在1/3、2/3附近。以行程速度与理想运送速度比值R_BF作为评价参数，当0≤R_BF<1/3时，公交系统处于拥堵状态；当1/3≤R_BF<2/3时，处于缓行状态；当2/3≤R_BF时，处于畅通状态。

关键词:交通工程;交通状态;公交运行状况;自然间断点法;城市异质性;速度比

Abstract:

To overcome the unstable results of bus operation status evaluation among different cities， the Natural Breaks was used to cluster the order statistics of bus travel speeds and determine the critical speed. The optimal classification of the bus operation state was determined according to the Goodness of Variance Fit and its increment. The critical speed， percentile， and ratio to bus free-flow speed are taken as the classification parameters to evaluate their stability. The research results show that： Dividing bus operation states into four categories is a sound choice， corresponding to the congested， slow， smooth， and free-flow states， and three critical speeds， e.g.， congestion， smooth， and free-flow speeds. The ratio between bus travel speed and free-flow speed should be the best parameter to recognize bus operation states. The ratios of the congestion and smooth speeds to the free-flow speed are 1/3 and 2/3， respectively. Taking the ratio between bus travel speed and free-flow speed R_BF as the evaluation parameter， when 0≤R_BF<1/3， the urban bus system is in congested status； when 1/3≤R_BF<2/3， it is in slow status； when 2/3≤R_BF， it is smooth.

Key words:traffic engineering;traffic state;bus operation status;natural breaks;city heterogeneity;speed ratio