随机行程时间下公交发车正点评价

Bus departure punctuality evaluation under stochastic travel time

公交运行过程受到外部行驶环境制约,服务可靠性评价需要考虑行程时间的波动.本研究建立了随机行程时间作用下始发站点发车偏差传播模型,发现了三个特征阈值,方向性累积站点停靠时间偏差阈值α,发车偏差不可修复阈值β,发车偏差恶化阈值γ,刻画了不同程度的发车偏差对下游站点服务可靠性退化程度的影响作用.从理论模型角度,证明任意站点n处三个阈值之间始终存在关系:αn<βn<γn;因此,随着始发站点发车偏差的加剧,下游站点位置首先产生方向性累积站点停靠时间偏差,进而造成发车偏差不可修复,最终导致发车偏差进一步恶化.从数值分析角度,发现在公交线路常规运营区域内(客流服务强度为0.20以内,线路长度为30 km以内),任意站点位置三个阈值之间始终存在关系:αn<βn<min(γ);因此,选择α或β作为发车正点评价阈值可以有效预防任意站点位置发车偏差的必定恶化.同时,阈值α相比β对客流服务强度敏感性更低,选择α作为评价依据能增强在不同线路条件下的普适性.为了充分利用随机行程时间下的服务偏差自主修复能力,且兼顾评价阈值的考核弹性,本研究最终推荐使用公交线路终点站位置的方向性累积站点停靠时间偏差阈值αN作为发车正点的评价标准.

The bus operation is significantly affected by its external driving environment,resulting in travel time variation;hence,the evaluation of bus service reliability should consider the influence of travel time variability.This research modeled the propagation of service deviation,which occurred at the start terminal,along the route under stochastic travel time.Three illustrative thresholds were found,namely the threshold of a cumulative directional deviation of dwell time(α),the threshold of an unrecoverable service deviation(β),and the threshold of a deteriorated service deviation(γ).They differentiate the degree of influence of the departure deviation at the start terminal on the service deviations at downstream stops.The theoretical model proved thatαn<βn<γn at any stop on the route.With the aggravation of the departure deviation at the start terminal,a cumulative directional deviation of dwell time occurs first,then an unrecoverable service deviation,and finally a deteriorative service deviation.The numerical results showed thatαn<βn<min(γ)always holds for any practical bus route with service intensities lower than 0.20 at stops and a route length shorter than 30 km.Therefore,takingαorβto regulate the punctuality of bus departure can prevent the deterioration of service deviation at any stop on the route.At the same time,the thresholdαis less sensitive to passenger service intensity thanβ;thus,choosingαas the evaluation standard can enhance the universality among bus routes with different levels of passenger demand.Finally,to make full use of the self-repair ability of bus routes under stochastic travel time and take into account the flexibility of evaluation thresholds,this study recommended the thresholdαN at the end terminal as a practical index to evaluate bus departure punctuality.