Traffic performance of shared lanes at signalized intersections based on cellular automata modeling

Shared lanes at signalized intersections are designed for use by vehicles of different movement directions. Shared lane usage increases the flexibility of assigning lane grouping to accommodate variable traffic volume by direction. However, a shared lane is not always beneficial as it can at time result in blockage that leads to both capacity and safety constraints. This paper establishes a cellular automata model to simulate traffic movements at signalized intersections with shared lanes. Several simulation experiments are carried out both for a single shared lane and for an approach with a shared lane. Simulation of a single shared lane used by straight‐through and right‐turn (as similar to left‐turn in the USA) vehicles suggests that the largest travel delay occurs when traffic volumes (vehicles/lane) of the two movement streams along the shared lane are at about the same level. For a trial lane‐group with a shared lane, when traffic volumes of the two movement streams are quite different, the shared lane usage is not efficient in terms of reduction in traffic delay. The simulation results are able to produce the threshold traffic volume to arrange a shared lane along an approach. Copyright © 2013 John Wiley & Sons, Ltd.     

基于元胞自动机的附加导流岛型出口仿真建模

为研究附加导流岛型出口对快速路交通流的影响，本文建立针对附加导流岛型出口的元胞自动机模型。基于KKW (Kerner Klenov Wolf)模型，引入3种换道规则并分段设定，以描述附加导流岛型出口影响下的车辆换道行为。针对主辅路直接衔接的几何特点，对主路车辆经由出口驶出的过程等效简化，定义附加导流岛型出口下的车辆驶出规则。模型的数值仿真结果表明：导流岛通过引导辅路车辆在导流岛上游向外侧车道合流，能够使辅路下游的内侧车道起到辅助车道的作用。在此设置下，辅路车流对车辆驶出造成的直接干扰得到缓解，主路的通行效率显著提高。然而，辅路车辆经过导流岛后的强制换道会对驶出的平稳交通流造成扰动而诱发局部拥堵， 影响驶出车流的进一步疏散，导致主路饱和流量和平均速度的下降。此外，导流岛使得辅路形成道路缩减瓶颈，在其影响下，辅路总饱和流量大幅下降。导流岛对辅路内侧车道的占用使得其流量和平均速度均低于外侧车道，通行效率受到更大的影响。     

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随着汽车拥有量的不断增加,公交站点对城市交通的影响日益突出, 对公交起迄点的研究,有助于公交站点的最优化布置,减少公交起迄点对道路交通的影响,提高公交起迄点路段的行车效率. 在Nagel-Schreckenberg交通流模型的基础上,采用双车道快车优先换道规则和开放边界条件,通过计算机模拟了公交车起讫站点车辆进出对城市双向四车道混合交通流的影响. 通过研究和分析发车时间间隔、车道注入概率和公交起迄站点位置对道路通行能力的影响,给出了比较合理的发车频率和公交起讫站点的位置,为改善城市道路交通和管理提供参考.     

设置非机动车等候区的信号交叉口交通流模型

城市机非混行交叉口的管理与控制是交通管理的重要内容.针对信号交叉口设置非机动车等候区的交通组织方式,建立了交叉口元胞自动机模型.对机动车流采用基于经典 NaSch(NS)的改进多车道元胞自动机模型,建立了交叉口换道规则,增加主动减速规则;对非机动车流采用具有侧向运动的扩展多值 CA模型.研究了设置等候区的车流状态特性,以及非机动车密度和等候区纵向长度对信号交叉口的影响.研究结果表明：设置等候区能在一定程度上提高交叉口的通行能力,但长度并非越长越好,当长度过长时在一定条件下会增大对机动车流的阻滞,总体上等候区是一种值得借鉴的方式;非机动车密度对机动车流的基本图具有显著影响.     

交通流元胞自动机模型综述

随着交通流模拟的需要及智能交通系统的发展,出现了基于元胞自动机理论的交通流模型。交通流元胞自动机模型由一系列车辆运动应遵守的运动规则和交通规则组成,并且包含驾驶行为、外界干扰等随机变化规则。文章介绍了交通流元胞自动机模型的产生与发展,总结和评述了国内外各种元胞自动机模型,并对元胞自动机模型的发展提出展望。     

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随着汽车技术的发展,道路上自动驾驶的车辆在未来会越来越多,给道路交通带来了巨大影响.本文引入了经典的Gipps安全距离规则,对Na Sch模型进行改进,提出了基于安全距离的自动驾驶元胞自动机交通流模型.然后,利用数值模拟的方法研究了自动驾驶车辆对道路交通流的影响,研究获得一些新的结论.第一,通过降低自动驾驶车辆系统的反应时间,可大幅提高道路通行能力,最高可达2倍.第二,当自动驾驶车辆系统的反应时间降到0.5 s以下时,其对道路通行能力的影响可忽略.第三,道路上自动驾驶车辆的比例对道路通行能力和交通拥堵有显著影响.当自动驾驶车辆的比例达到80%时,通行能力可达到全手动驾驶交通流的2倍,交通拥堵可以降低50%.第四,在全自动驾驶的交通流中,增大自动驾驶反应时间会减少交通拥堵.特别是当密度在30~60 veh/km的范围内时作用更为明显,拥堵比例下降最高可达到20%,可以作为一种缓解拥堵的策略.     

The brittleness model of complex system based on cellular automata

Now the research on the complex system is a hot spot. Brittleness is one of the basic characteristics of a complex system. In a complex system, after one of subsystems is struck to be collapsed, the whole system will collapse. Meanwhile, cellular automata is a discrete dynamic system. When the rule is given, the cellular automata could be defined. Then it can imitate the complex action. Cellular automata is used to simulate the brittleness action in this study. Entropy was used to analyze the action and get the rule. Then,three normal brittleness models were given. The result shows that the brittleness of complex system is existent and in addition some important behavior mode of complex system brittleness has been achieved.     

A practical identifier design of road variations for anti-lock brake system

Emergency brake technologies have always been a major interest of vehicle active safety-related studies. On homogeneous surfaces, traditional anti-lock brake system (ABS) can achieve efficient braking performance and maintain the handling capability as well. However, when road conditions are time variant during the braking process, or different at the bilateral wheels, braking stability performance is likely to be degraded. To address this problem and enhance ABS performances, a practical identifier of road variations is developed in this study. The proposed identifier adopts a statechart-based approach and is hierarchically constructed with a wheel layer and a full vehicle layer identifier. Based on the identification results, modifications are made to a four-phase wheel-behaviour-based ABS controller to enhance its performance. The feasibility and effectiveness of the proposed identifier in collaborating with the modified ABS controller are examined via simulations and further validated by track tests under various practical braking scenarios.     

考虑双向交通的城市路网交通流元胞自动机模型

允许车辆借反向车道超车的双向交通道路是城市路网的重要组成部分.本文考虑了双向交通道路的车辆行驶规则,研究了无信号控制交叉口的车辆优先通行权分配规则,构建了一个双向交通的城市路网交通流元胞自动机模型,研究了城市路网交通流的动态特性.研究结果表明,临界密度随着路网规模的增加而下降,路网交通密度的增加会加速拥堵闭环的形成,换道概率的增加会降低路网车速和缩短局部死锁现象形成的时间,单位时间换道车辆数与换道概率及交通密度之间存在着密切的关系.     

交通态势识别及状态转换机制研究

利用驾驶员的认知拓扑生成动态交通态势图,以克服驾驶员视野盲区的缺陷,可进一步避免交通事故的发生,为交通运输系统和智能车辆系统的仿真研究和实物开发提供理论指导与技术支持.