Siting park-and-ride facilities using a multi-objective spatial optimization model

Park-and-ride services are an important component of many public transportation systems in the United States. Locating park-and-ride facilities is an essential step when planning for these services. In this research we focus on three major siting/modeling concerns that need to be addressed when siting park-and-ride facilities: covering as much potential demand as possible, locating park-and-ride facilities as close as possible to major roadways, and siting such facilities in the context of an existing system. Unfortunately, existing models do not enable each of these concerns to be simultaneously addressed. This paper presents a multi-objective spatial optimization model for integrating these considerations. This model is applied for siting park-and-ride facilities in Columbus, Ohio. Application results show the usefulness of the developed model in supporting transit planning in an urban region.     

Adaptive Park-and-ride Choice on Time-dependent Stochastic Multimodal Transportation Network

In transportation networks with stochastic and dynamic travel times, park-and-ride decisions are often made adaptively considering the realized state of traffic. That is, users continue driving towards their destination if the congestion level is low, but may consider taking transit when the congestion level is high. This adaptive behavior determines whether and where people park-and-ride. We propose to use a Markov decision process to model the problem of commuters’ adaptive park-and-ride choice behavior in a transportation network with time-dependent and stochastic link travel times. The model evaluates a routing policy by minimizing the expected cost of travel that leverages the online information about the travel time on outgoing links in making park-and-ride decisions. We provide a case study of park-and-ride facilities located on freeway I-394 in Twin Cities, Minnesota. The results show a significant improvement in the travel time by the use of park-and-ride during congested conditions. It also reveals the time of departure, the state of the traffic, and the location from where park-and-ride becomes an attractive option to the commuters. Finally, we show the benefit of using online routing in comparison to an offline routing algorithm.

     

基于Anylogic的轨道交通换乘能力改进的研究

研究轨道交通换乘枢纽与市内其它交通方式的衔接与协调,是城市公共交通线网优化的主要内容之一。它能减少出行过程中的等待时间,缩短人们出行时间,提高公交服务质量,并保证客运交通的高效率,也能更好地促进城市轨道交通与其它交通方式的协调发展。以武汉地铁某换乘站研究对象,通过实地采集其基本设施的位置和数量、入站行人和出站行人的数量,并利用Anylogic仿真软件,建立站点的平面布置图空间模型和行人流程图。首先通过仿真软件仿真找出换乘客流瓶颈部位,其次分别对其提出改善建议并加以修改仿真模型。最终仿真结果表明,改善建议使得换乘站的换乘效率都得到提高。     

无线Mesh网在城市轨道交通车地通信系统中的研究

无线Mesh网因组网灵活、支持范围大和移动性强等特点,使其在城市轨道交通(城轨)中具有很好的应用前景。尝试将无线Mesh网技术应用于城轨车地通信系统中,针对车地通信存在的越区切换问题,提出了一种基于车载MMS(mobile Mesh station)位置触发的越区切换方案,利用OPNET对组网方案和切换方案进行了仿真。仿真结果表明,无线Mesh组网方案性能优于传统WLAN组网方案性能,切换方案能有效降低时延并避免了假切换和乒乓切换的发生。     

The Vanpool Assignment Problem: Optimization models and solution algorithms

We present optimization models and solution algorithms for the Vanpool Assignment Problem. A vanpool is typically a group of 9-15 passengers who share their commute to a common target location (typically an office building or corporate campus). Commuters in a vanpool drive from their homes to a park-and-ride location where they board a van and ride together to the target location; at the end of the work day they ride together back to the park-and-ride location. The Minimum Cost Vanpool Assignment Model (MCVAM) developed in this study is motivated by a program offered by Gulfstream Aerospace, a large employer in the Dallas/Fort-Worth area, Dallas Area Rapid Transit (DART), and Enterprise Rent-A-Car. Our MCVAM imposes constraints on the capacity of each van and quality-of-service constraints on the cost and travel time involved in joining a vanpool. The goal of the MCVAM is to minimize the total cost of a one-way trip to the target location for all employees (including those employees who opt-out of the program and choose not to join a vanpool). To the best of our knowledge, this is the first mathematical programming model proposed for the standard (one-stop) Vanpool Assignment Problem. The MCVAM models the current practice in vanpooling of using one park-and-ride location per vanpool. We also present a Two-Stop MCVAM (TSMCVAM) that offers significant cost savings compared to the MCVAM with little or no increase in trip times for most passengers by allowing vanpools to stop at a second park-and-ride location. We present heuristics for the TSMCVAM which are shown in a computational study to find solutions with optimality gaps ranging from 5% to 10% in CPU times ranging from 1 to 15 min for problem instances with up to 600 employees and 120 potential park-and-ride locations.     

基于负载系数的轨道交通网络控制站点辨识

城市轨道交通客流量对轨道交通运行的效率与安全至关重要.利用客流信息,提出负载系数衡量网络负载情况,并作为轨道交通网络边的权重,建立轨道交通网络模型.运用复杂网络的可控性理论分析轨道交通网络的可控性问题,给出轨道交通网络控制节点的辨识方法,实现对城市轨道交通网络限流车站的控制.以北京地铁网络为实例建立携带负载系数的网络模型,对其控制节点的选取进行分析,结果表明现行常态化控制站点不能使网络完全可控,且选择的控制站点数量较多,成本较高,应用负载系数作为权重选择的限流站点不仅能够使网络完全能控选择的控制站点数量更少,成本较低,而且更多地分布于超载线路上,同时所提出方法可以有效找出控制站点,为实际限流车站的选取提供有效的参考.     

Bus-based park-and-ride system: a stochastic model on multimodal network with congestion pricing schemes

This paper focuses on modelling the network flow equilibrium problem on a multimodal transport network with bus-based park-and-ride (P&R) system and congestion pricing charges. The multimodal network has three travel modes: auto mode, transit mode and P&R mode. A continuously distributed value-of-time is assumed to convert toll charges and transit fares to time unit, and the users’ route choice behaviour is assumed to follow the probit-based stochastic user equilibrium principle with elastic demand. These two assumptions have caused randomness to the users’ generalised travel times on the multimodal network. A comprehensive network framework is first defined for the flow equilibrium problem with consideration of interactions between auto flows and transit (bus) flows. Then, a fixed-point model with unique solution is proposed for the equilibrium flows, which can be solved by a convergent cost averaging method. Finally, the proposed methodology is tested by a network example.     

基于宁波城乡结合部的轨道交通接驳常规公交线网优化研究

为提高大都市城乡结合部道路网的交通运行效率,选取宁波市城乡结合部区域,针对轨道交通节点与常规公交的自适应接驳问题,考虑到公交线网的日均满载率、线路的客运能力、线网的重复性、客流负载率等约束条件,运用ARCGIS软件强大存储与计算能力、良好的线网叠加能力以及优化网络拓扑节点不间断的客流检测分析,并基于宁波市城乡结合部交通规划建设背景,探索宁波市城乡结合部轨道交通与公交线网协调优化关系以及两者的接驳形态。综合运用可达性方法、最短线路标记法等,研究宁波市城乡结合部交通线网在站点、线网运营等方面的协调优化机制;并进一步对宁波市城乡结合部公交线网接驳轨道交通网优化结果进行可视化。实验证明优化后的宁波市城乡结合部交通线网优于现行的策略方案。本研究模型调度策略能够为宁波市城乡结合部的交通管制部门提供可靠的公交线网优化方案,并为其他城市的城乡结合部制定正确的交通调控政策提供科学依据。     

基于人工免疫算法的交通时段自动划分方法

多时段定时控制是城市交通信号控制的重要方式之一,交通时段的合理划分是制定多时段定时控制方案的基础.为克服传统时段划分方法的局限性,实现城市交通时段的自动划分,论文提取生物免疫系统的隐喻机制,基于免疫网络理论和克隆选择原理,建立了一种人工免疫数据聚类分析算法,并详细阐述了聚类算法在城市交通时段自动划分中的具体应用.实例分析表明,该算法可以有效减少聚类数据的冗余信息,特别适合于解决分级聚类等传统方法不适应的大数据量聚类问题,对解决城市交通时段的自动划分等数据聚类问题是可行的和有效的.     

城市交通网络宏观控制模型及仿真实现

为研究适合城市交通网络控制系统应用的交通流预测模型,在改进Van Den Berg, M的路段交通流模型的基础上,建立了以路口交通流为基本建模单元,以动态非线性离散方程反映交通流变化的城市交通网络宏观模型.为验证该模型能有效地预测城市路网的交通流信息,在VC++net环境下,开发了城市交通宏观控制模型仿真系统UTFS,设计了网络拓扑结构模块,以适应不同规模、不同复杂程度的实际交通网络的仿真要求.最后选取典型网络进行应用研究.仿真结果表明:该模型满足交通控制对控制模型的实时性和精度要求,该仿真系统可以作为城市交通网络宏观控制模型验证的有效工具,也可以作为城市交通控制系统控制和优化研究的辅助工具.     

Evaluating Dynamic Task Mapping in Network Processor Runtime Systems

Modern network processor systems require the ability to adapt their processing capabilities at runtime to changes in network traffic. Traditionally, network processor applications have been optimized for a single static workload scenario, but recently several approaches for runtime adaptation have been proposed. Comparing these approaches and developing novel runtime support algorithms is difficult due to the multicore system-on-a-chip nature of network processors. In this paper, we present a model for network processors that can aid in evaluating different runtime support systems. The model considers workload characteristics of applications and network traffic using a queuing network abstraction. The accuracy of this analytical approach to modeling runtime systems is validated through simulation. We illustrate the effectiveness of our model by comparing the performance of two existing workload adaptation algorithms.     

A survey on two-echelon routing problems

The delivery of freight from its origin to its destination is often managed through one or more intermediate facilities where storing, merging and consolidation activities are performed. This type of distribution systems is commonly called multi-echelon, where each echelon refers to one level of the distribution network. Multi-echelon distribution systems are often considered by public administrations when implementing their transportation and traffic planning strategies as well as by private companies in their distribution networks. City logistics and multi-modal transportation systems are the most cited examples of multi-echelon distribution systems. Two-echelon distribution systems are a special case of multi-echelon systems where the distribution network comprises two levels. This latter type of distribution systems has inspired an ever growing body of literature in the last few years. This paper provides an overview of two-echelon distribution systems where routes are present at both levels. We consider three classes of problems: the two-echelon location routing problem, the two-echelon vehicle routing problem, and the truck and trailer routing problem. For each class we provide an introduction and survey the foremost related papers that have appeared in the operations research literature.     

Distributed Model Predictive Control Method for Optimal Coordination of Signal Splits in Urban Traffic Networks

Coordination and control approaches based on model predictive control (MPC) have been widely investigated for traffic signal control in urban traffic networks. However, due to the complex non‐linear characters of traffic flows and the large scale of traffic networks, a basic challenge faced by these approaches is the high online computational complexity. In this paper, to reduce the computational complexity and improve the applicability of traffic signal control approaches based on MPC in practice, we propose a distributed MPC approach (DCA‐MPC) to coordinate and optimize the signal splits. Instead of describing the dynamics of traffic flow within each link of the traffic network with a simplified linear model, we present an improved nonlinear traffic model. Based on the nonlinear model, an MPC optimization framework for the signal splits control is developed, whereby the interactions between subsystems are accurately modeled by employing two interconnecting constraints. In addition, by designing a novel dual decomposition strategy, a distributed coordination algorithm is proposed. Finally, with a benchmark traffic network, experimental results are given to illustrate the effectiveness of the proposed method.     

Agent-based approach to analyzing the effects of dynamic ridesharing in a multimodal network

An agent-based modeling for dynamic ridesharing in a multimodal network is proposed in this paper. The study aims to evaluate the performance of dynamic ridesharing system within a multimodal network and explore the competing mechanism between dynamic ridesharing and public transit, with the presence of managed lane facility. The modeling process simulates the interaction between travelers and the network, and applies a heuristic algorithm to model travelers' decision making process under uncertainty. The model is applicable to networks with varying demographics. Multiple scenarios based on the classic Sioux Falls network have been examined. The modeling results demonstrate that the effects of dynamic ridesharing on a network differ with traffic demand and market penetrations of various travel modes. In networks with high travel demand and low market penetration of public transit, the benefits of dynamic ridesharing system on reducing congestion and providing reliable travel time are quite limited. To enhance the effectiveness of dynamic ridesharing, traffic operators may consider project investments on managed lane facilities. In networks with high market penetration of public transit, dynamic ridesharing may attract large amounts of short distance trips and aggravate congestion, especially at the initial launching phase. Policy makers would want to ensure that the existing infrastructure is sufficient to accommodate the extra traffic induced by ridesharing. Ridesharing service providers might also consider proper strategies to avoid “abuse” of the system by short trips and accelerate the market penetration.     

城市智能公共交通系统模型框架的设计与研究

传统的城市公交系统已经不能保障城市公共交通的顺畅运行.为适应当今的交通需要和响应国家"十一五"规划,提出并介绍一个城市智能公共交通系统模型框架及其主要功能模块.该系统有效解决了城市目前面临的交通问题,为建立城市大规模完整的智能交通系统提供了有力支撑.     

Check方式轨道交通调度监督系统的设计与实现

针对轨道交通信号系统的特点,文章提出了一种基于Check方式的城市轨道交通调度监督系统。结合上海明珠线调度监督系统,介绍了系统数据库的事务处理和并发控制,给出了几种优化系统的措施,以及系统的软件结构和系统功能。     

A multi-objective optimization approach for health-care facility location-allocation problems in highly developed cities such as Hong Kong

Public health-care facilities are essential to all communities, and their location/allocation has long been an important issue in urban planning. Given the steady growth of Hong Kong's population, new health-care facilities will need to be built over the next few years. This research examines the problem of where such health-care facilities should be located to improve the equity of accessibility, raise the total accessibility for the entire population, reduce the population that falls outside the coverage range, and decrease the cost of building new facilities. However, because urban areas such as Hong Kong are complex socio-ecological systems, the aforementioned conflicting objectives make it impossible to find one ‘best’ solution that meets all of the objectives. Therefore, this research uses a genetic algorithm based multi-objective optimization (MOO) approach to yield a set of Pareto solutions that can be used to find the most practical tradeoffs between the conflicting objectives. The MOO approach is used to optimize the location of new health-care facilities in Hong Kong for 2020. Because the MOO approach provides a set of diverse plans, planners can compare the value of each objective and the spatial distribution of facilities to analyze or select the solution that best supports their further decisions. Comparing the Pareto solutions with other solutions, it indicates that the MOO approach is a sensible choice for solving multi-objective problems of health-care facility location-allocation in Hong Kong.     

路网分区的树生长算法*

分析和定义了面向城市交通控制系统交通控制方案制订的路网分区需要解决的问题,设计了动态路网分区概念模型。针对路网交通小区根生节点问题的解决,设计了路网节点重要度判断算法;以根生节点为中心,采用逐层扫描技术对节点交通流作用路径进行搜索,形成路网小区的拓扑结构图。以一个实际城市交通网络为例,利用提出的模型及算法进行分区,结果表明了算法的有效性和可行性。     

Optimally designing caches to reduce P2P traffic

Traffic caused by P2P services dominates a large part of traffic on the Internet and imposes significant loads on the Internet, so reducing P2P traffic within networks is an important issue for ISPs. In particular, a huge amount of traffic is transferred within backbone networks; therefore reducing P2P traffic is important for transit ISPs to improve the efficiency of network resource usage and reduce network capital cost. To reduce P2P traffic, it is effective for ISPs to implement cache devices at some router ports and reduce the hop length of P2P flows by delivering the required content from caches. However, the design problem of cache locations and capacities has not been well investigated, although the effect of caches strongly depends on the cache locations and capacities. We propose an optimum design method of cache capacity and location for minimizing the total amount of P2P traffic based on dynamic programming, assuming that transit ISPs provide caches at transit links to access ISP networks. We apply the proposed design method to 31 actual ISP backbone networks and investigate the main factors determining cache efficiency. We also analyze the property of network structure in which deploying caches are effective in reducing P2P traffic for transit ISPs. We show that transit ISPs can reduce the P2P traffic within their networks by about 50-85% by optimally designing caches at the transit links to the lower networks.     

基于GPS/PDA的城市排水管网巡检管理平台

针对排水系统设施众多、系统数据量庞大的问题,设计出基于GPS/PDA的城市排水管网巡检管理集成平台。该平台集成地理信息系统(GIS)和无线通信技术,利用智能手机/PDA将设备运行状况和巡检车辆位置通过GPRS上传到监控中心服务器中,服务器将指令发送回PDA终端,为巡检工作提供方便。采用GPS全球定位技术,对PDA的地理位置进行精确定位、跟踪、查询,保证数据传输的准确、高效和安全。在常州市排水管网的实际应用中,该平台能够有效地加强对排水设施的维护、抢修以及对巡检车辆的管理,及时应对出现的问题,提高巡检工作效率,从而为城市排水系统建设与维护工作提供科学的管理手段。