Planning hierarchical urban transit systems for reductions in greenhouse gas emissions

Public transit systems with high occupancy can reduce greenhouse gas (GHG) emissions relative to low-occupancy transportation modes, but current transit systems have not been designed to reduce environmental impacts. This motivates the study of the benefits of design and operational approaches for reducing the environmental impacts of transit systems. For example, transit agencies may replace level-of-service (LOS) by vehicle miles traveled (VMT) as a criterion in evaluating design and operational changes. In previous work, we explored the unintended consequences of lowering transit LOS on emissions in a single-technology transit system. Herein, we extend the analysis to account for a more realistic case: a transit system with a hierarchical structure (trunk and feeder lines) providing service to a city where demand is elastic. By considering the interactions between the trunk and the feeder systems, we provide a quantitative basis for designing and operating integrated urban transit systems that can reduce GHG emissions and societal costs. We find that highly elastic transit demand may cancel emission reduction potentials resulting from lowering LOS, due to demand shifts to lower occupancy vehicles. However, for mass transit modes, these potentials are still significant. Transit networks with buses, bus rapid transit or light rail as trunk modes should be designed and operated near the cost-optimal point when the demand is highly elastic, while this is not required for metro. We find that the potential for unintended consequences increases with the size of the city. Our results are robust to uncertainties in the costs and emissions parameters.     

The potential mitigation of CO2 emissions via modal substitution of high-speed rail for short-haul air travel from a life cycle perspective – An Australian case study

The objective of this study is to provide a strategic evaluation of the mitigation of CO₂ emissions via modal substitution of high-speed rail for short-haul air travel on the Sydney–Melbourne, Australia city-pair from a life cycle perspective. It has been demonstrated that when considering CO₂ emissions from vehicle operations, the modal shift from air to high-speed rail on this city-pair has the potential to provide a means of CO₂ mitigation. However, uncertainty exists with regard to the level of mitigation potential when considering the whole-of-life performance of the systems. Given the significant difference in the infrastructure requirements between the air mode and the high-speed rail mode, this study quantifies the life cycle CO₂ load attributable to each system and examines the effect on CO₂ mitigation potential. The study concluded that while the inclusion of the linehaul infrastructure did increase the CO₂ load associated with high-speed rail mode, it did not equate to or exceed the CO₂ load per trip as experienced by the air mode. The avoided annual life cycle CO₂ emission in the target year 2056 was 0.37 Mt representing an 18% reduction when compared to the air mode only on the city pair. In fact, the scenario comparison indicated that the substitution of high-speed rail for short-haul air travel on the city pair resulted in CO₂ emissions avoidance throughout the longitudinal period.     

轨道交通接运公交专线现状特性分析

文章通过对广州市地铁接运公交专线现状的调研,分析了我国大城市轨道交通接运公交的现状特性及影响其运营性能的各种因素,探讨了提高运营性能的方法,为类似城市轨道交通接运公交专线的规划提供参考。     

城市轨道交通中个人导向方法研究

文章运用层次分析的方法来阐述个人导向功能的实现原理,提出了利用现阶段飞速发展的移动通信体技术,设计一种应用在城市轨道交通中具有个人导向功能的移动通信体,以改善城市轨道交通中个人导向功能薄弱的现状。     

Development and validation of a direct mode choice model

A direct discrete mode choice model is introduced using relative attributes of competing modes as well as socioeconomic characteristics of travelers. The model is calibrated and validated for two available historic databases in the Dallas–Fort Worth region. The validation is conducted against the outputs of a current nested logit model used by the regional planning organization as well as the observed values based on transit ridership surveys for a newly inaugurated commuter rail service. The calibrated model is applied after the introduction of this new transit mode. The results show that the estimated mode shares by the proposed model have a statistically better consistency with the observed values than the estimates of the conventional nested logit model. Unlike the logit model, the structure of the direct model based on relative attributes also has the advantage of not needing recalibration each time a new travel mode is introduced. The model is found to be easier to calibrate and produces more accurate results than the nested logit model, commonly used by many metropolitan planning organizations.     

The effect of crowding on public transit user travel behavior in a large-scale public transportation system through modeling daily variations

In this paper, the crowding effect in a transit vehicle is modeled in a time-expanded network that considers the daily variation in passenger flows. The study models the daily variation of in-vehicle crowding in a real large-scale transit system. A transit assignment for this real network is modeled and implemented by constructing a crowding cost function that follows the valuation of crowding and by using the reliable shortest path finding method. The direct application of the crowding model to a real network for the Utah Transit Authority indicates that crowd modeling with multi-user classes could influence public transportation system planning and affect the revenues of transit agencies. Moreover, the addition of the disutility factor, crowding, does not always appear to cause an increase in disutility for transit users.     

基于虚拟编组的城轨列车时刻表优化方法

针对高峰时段城市轨道交通客流与运力不匹配问题,考虑城市轨道交通客流时空分布特征、交通过饱和状态和车场车底数量限制,提出了基于虚拟编组的城轨列车时刻表优化方法。构造动态客流累计需求函数,预测不同时段客流量;考虑乘客需求、发车间隔、运行时间、车底数量、车底接续等约束条件,以列车在首站的发车时刻和各车次的编组方案为决策变量,以乘客平均等待时间与列车走行里程最小化为优化目标,建立了基于虚拟编组的城轨列车时刻表优化模型。针对原问题包含大量耦合约束条件,利用拉格朗日松弛算法将耦合性约束吸收至目标函数,将原问题分解为2个独立路径的子问题,降低问题的复杂度;再利用商业求解器求解子问题的下界解,并设计启发式算法求解子问题的上界可行解,得到原问题解的上下界。以上海地铁某线路为算例进行验证,结果表明：在高峰时段,所提动态客流累计需求函数与客流实际到达规律拟合度较高;固定编组模式下,非均匀发车时刻表相比于均匀发车时刻表,可降低24.15%的乘客平均等待时间和51.73%的滞留乘客等待时间;而所提虚拟编组列车时刻表相比于固定编组模式下非均匀发车时刻表,不仅可减少0.33%的列车运行里程,还可进一步减少16.95%的乘客平均等待时间和6.03%的滞留乘客等待时间。     

城市轨道交通系统韧性研究现状及展望

具有良好韧性水平的城市轨道交通系统能够有效应对因自然灾害、人为失误、设施设备故障等因素导致的突发事件。为充分把握国内外城市轨道交通系统韧性相关的研究动态,运用文献计量分析法分析了相关研究文献的关键词和研究热点,发现早期的研究重点为轨道硬件结构韧性,运营服务韧性在近年来逐渐得到关注。结合韧性概念在物理学领域、生态学领域和城市管理领域的发展过程,阐释了城市轨道交通韧性的内涵。面向典型的社会事件和自然灾害场景,韧性评估方法的研究对象由车站扩展至线路再到线网,但在当前技术条件下评估对象的规模与颗粒度存在博弈关系,尚未完全挖掘宏微观、动静态对象间的联动影响机理。在韧性评估指标方面,对基于拓扑结构、运输能力、综合性能和业务环节的指标体系进行梳理,发现还可进一步从空间布局、工程条件、设施设备、人员配置、管理手段、社会力量等方面丰富现有指标体系。在指标度量方面,梳理了基于性能曲线的韧性建模、大数据分析、仿真模拟和数值分析共4种典型方法,发现基于单一方法的度量结果易受数据量、假设条件、指标权重分配等因素的影响,应综合使用多种方法度量不同类型和评估阶段的指标。在韧性提升和恢复方面,总结了包含事前预防、事中适应和事后恢复阶段的策略,发现既有研究多从运营管理角度出发,城市轨道交通基础设施灾后恢复的相关研究处于初步探索阶段。最后从①提升突发场景建模真实性;②考虑沿线城市空间和功能的影响进行动态细粒度分析;③探究突发事件影响传播机理以刻画系统内部变化;④研究韧性评估与提升效果验证方法共4个方面展望未来轨道交通系统韧性研究的发展方向。