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.     

时速350 km中国标准动车组车载天线的隔离度及最小排布间距

基于中国标准动车组车载终端设备的部署现状和未来规划,调研其采用的通信系统类型、车载天线的工作频率和安装数量;以900MHz频段GSM-R系统、450MHz频段和2 100MHz频段LTE-R系统为例,对车载终端的杂散干扰进行理论分析,基于自由空间损耗理论模型计算、电磁软件仿真模拟和试验平台实测的结果,研究车载天线的隔离...     

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。     

基于回流电感应电源的研究与应用

利用电气化铁路架空回流线与大地间的电位差研制的高压感应电源,有效地解决了铁路沿线尤其是隧道内对交流电源的需要,使一些智能监控设备得以在铁路沿线安装使用。介绍回流电感应电源的工作原理、技术参数、性能特点。     

城市组团的轨道交通接驳线研究

城市外围组团快速发展,需要较大运量的接驳线快速衔接城市轨道交通资源,同时缓解组团内日益增长的交通压力。从接驳线的功能定位、规划条件、制式比选及衔接模式等方面进行分析,并以天津空港经济区为例进行较为系统的说明。中低运量的轨道交通系统和BRT(快速公交系统)均能满足接驳线的需求。接驳线的建设应在发挥现有公共交通能力的基础上进行充分论证,不宜过度超前;采用轨道交通系统时要处理好同既有轨道交通线网的关系。     

Evolution of public transit modes in a commuter corridor

This paper explores how the selection of public transit modes can be optimized over a planning horizon. This conceptual analysis sacrifices geographic detail in order to better highlight the relations among important factors. First, a set of static models is proposed to identify which type of service, e.g., bus only, rail only, or bus and rail, is the most cost-effective in terms of the average trip cost for given demand. After analyzing essential factors in a long-term planning process, e.g., economies of scale in rail extension and future cost discounting, a dynamic model incorporating such considerations is formulated to optimize the decision over a planning horizon. While analytical solutions can be obtained for some decision variables, the final model is solved with a graphical method by exploring the tradeoffs between the initial and recurring costs. Major findings from this study include: (a) there exists a minimum economic length for a rail line, which can be determined numerically; (b) economies of scale favor large extensions and excess supplied capacity; (c) the rail-only service is largely dominated by the feeder-trunk service, even in the long run.     

A methodology to derive the critical demand density for designing and operating feeder transit services

Feeder lines are one of the most often used types of flexible transit services connecting a service area to a major transit network through a transfer point. They often switch operations between a demand responsive and a fixed-route policy. In designing and running such systems, the identification of the condition justifying the operating switch is often hard to properly evaluate. In this paper, we propose an analytical model and solution of the problem to assist decision makers and operators in their choice. By employing continuous approximations, we derive handy but powerful closed-form expressions to estimate the critical demand densities, representing the switching point between the competing operating policies. Based on the results of one-vehicle and two-vehicle operations for various scenarios, in comparison to values generated from simulation, we verify the validity of our analytical modeling approach.     

Built environment effects on the integration of dockless bike-sharing and the metro

Bike-sharing provides a convenient feeder mode for connecting to a metro and is believed to be an efficient way to solve the first- and last-mile problem. Despite the increasing attention paid on the use of bike-sharing, few studies have investigated how built environment factors affect the integrated use of dockless bike-sharing (DBS) and the metro. Using data from one of the largest DBS operators in China (Ofo), this paper employed a series of negative binomial regressions to examine the effect of the built environment on the integrated use of DBS and the metro, using Shenzhen as a case study. The findings show that mixed land use is positively related to integrated use. Residential areas have higher access-integrated rates during the morning peak hours, while industrial areas are associated with more integrated uses, connecting factories and metro stations. Furthermore, parks and public squares encourage both access- and egress-integrated use during peak times. Transportation facility features, including bus stops and dedicated bike lanes, are positively related to integrated use, while areas with dense metro distribution and main streets with many intersections are negatively related. Transfer distance also plays a crucial and negative role in integrated use. In addition, metro stations that are closer to the city center with a higher number of passengers are more likely to be integrated with bike-sharing. These findings can be used to collectively facilitate a connection between cycling and metro transit by creating a bicycle-friendly environment.     

Impact assessment of the Internet of Things on feeder transit performance

ABSTRACT

Efficient planning for demand responsive transit (DRT) can contribute to fulfilling the first/last mile transport needs for users of a major transit line. With the advancement in communication technologies, the internet is expected to assist this growing need of providing first/last mile connectivity. This is proposed to be achieved through a network created by Internet of Things (IoT). This paper evaluates the effect of implementation of IoT on service quality (or disutility) of DRT for two scenarios – with enabled-IoT (e-IoT) and with disabled-IoT (d-IoT). Data from five different DRT-like systems known as Call-n-Ride (CnR) routes operating in Denver, Colorado, are used for evaluation purposes. These CnR routes are Meridian, Interlocken, South Inverness, Broomfield and Louisville. Results show that, in general, all CnR routes would experience more than a 58 percent decrease in disutility if their operations were based on ‘with e-IoT’ operations. Interlocken would record the largest percentage decrease (74 percent) in disutility if its route service switched from the ‘with d-IoT’ to the ‘with e-IoT’ scenario.     

A new street connectivity indicator to predict performance for feeder transit services

This paper defines a novel street Connectivity Indicator (C.I.) to predict transit performance by identifying the role that street network connectivity plays in influencing the service quality of demand responsive feeder transit services. This new C.I. definition is dependent upon the expected shortest path between any two nodes in the network, includes spatial features and transit demand distribution information and is easy to calculate for any given service area. Simulation analyses over a range of networks have been conducted to validate the new definition. Results show a desirable monotonic relationship between transit performance and the proposed C.I., whose values are directly proportional and therefore good predictors of the transit performance, outperforming other available indicators, typically used by planners.