Simulation of traffic flow with traffic light strategies via a modified cellular automaton model

Traffic flows controlled by traffic light strategies were investigated via a cellular automaton model with anticipation, which is suitable for describing urban traffic. Three kinds of strategies, i. e., synchronized, green-wave and random switching lights, were designed, simulated and compared with each other. It is shown that the green-wave strategy is only valid at lower density and there is not an effective way with the three strategies to improve the efficiency of traffic flow at high density.

A Modified Cellular Automaton Model for Traffic Flow

A modified cellular automaton model for traffic flow was proposed. A novel concept about the changeable security gap was introduced and a parameter related to the variable security gap was determined. The fundamental diagram obtained by simulation shows that the maximum flow more approaches to the observed data than that of the NaSch model, indicating that the presented model is more reasonable and realistic.

Instantaneous information propagation in free flow,synchronized flow,stop-and-go waves in a cellular automaton model

Recently, a number of efforts are underway to investigate inter-vehicle communications （IVC）. This paper studies the instantaneous information propagation behaviours based on IVC in three different tragic situations （free flow, synchronized flow and stop-and-go waves） in a cellular automaton model. It is shown that different behaviours appear in stop-and-go waves from those in free flow and synchronized flow. While the distribution of Multi-hop Communication Distance （MhCD） is either exponential or uniform in free flow and synchronized flow, the distribution of MhCD is either exponential or with a single peak in stop-and-go waves.

Steady state speed distribution analysis for a combined cellular automaton traffic model

Cellular Automaton （CA） based traffic flow models have been extensively studied due to their effectiveness and simplicity in recent years. This paper develops a discrete time Markov chain （DTMC） analytical framework for a Nagel-Schreckenberg and Fukui Ishibashi combined CA model （W^2H traffic flow model） from microscopic point of view to capture the macroscopic steady state speed distributions. The inter-vehicle spacing Maxkov chain and the steady state speed Markov chain are proved to be irreducible and ergodic. The theoretical speed probability distributions depending on the traffic density and stochastic delay probability are in good accordance with numerical simulations. The derived fundamental diagram of the average speed from theoretical speed distributions is equivalent to the results in the previous work.

Generalized Anticipation Effect Models for Traffic Flow

Taking into account the startup behaviour of following vehicles in the waiting area of urban traffic signal, we propose an extended Nagel-Schreckenberg model for single-lane traffic flow, in which the dynamic behavior of each vehicle depends on not only its own headway but also the headway of the immediately preceding one. The numerical simulation of the present model reproduces some complicated nonlinear phenomena observed in real traffic such as free flow, ghostly blockage, synchronized flow and so on. For specific parameter combinations the flow-density relation of this model shows two meta-stable branches near the transition density from free flow to wide moving traffic jam. Finally, the analytical results of the model under some specific parameters are given by using the mean field theory.

Traffic flow of a roundabout crossing with an open boundary condition

This paper presents a cellular automaton traffic flow model with an open boundary condition to describe the traffic flow at a roundabout crossing with an inner roundabout lane and an outer roundabout lane. The simulation results show that the boundary condition, bottlenecks and the self-organization affect the traffic flow at the roundabout crossing. Because of the effect of bottlenecks, jams easily appear on the inner roundabout lane. To improve the capacity of the roundabout system, proper values of the enter probability α and the out probability βcan be chosen.

考虑CAV与公交车比的混合交通流特性

为探究网联环境下汽车和公交车组成的混合交通流特性,考虑驾驶员行为改进Gipps安全距离规则,结合美国path实验室提出的自适应巡航(Adaptive Cruise Control,ACC)、协同自适应巡航(Cooperative Adaptive Cruise Control,CACC)跟驰模型加速度定义,构建异质流元胞自动机模型。通过数值仿真实验,分析网联自动驾驶车辆(Connected Autonomous Vehicles,CAV)与公交车辆混入比例对交通流通行能力、行驶速度、道路拥堵的影响。结果表明:随着CAV比例的提高,道路通行能力增大,临界密度增大;当道路上车辆组成仅为CAV车辆时,通行能力提升2.45倍、临界密度提高2.84倍;当CAV比例为0.5,随着公交车比例的增加,道路随机多发的轻微拥堵明显减少,通行能力、平均行驶速度略微减小。网联车能有效提高道路通行能力和行驶速度、减少拥堵,且随着公交车比例的提高,网联公交车更易形成队列,使道路拥堵得到明显改善。

A weighted mean velocity feedback strategy in intelligent two-route traffic systems

Information feedback strategies can influence the traffic efficiency of intelligent traffic systems greatly.Based on the more practical symmetrical two-route scenario with one entrance and one exit,an improved weighted mean velocity feedback strategy（WMVFS） is proposed,which is not sensitive to the precision of global position system（GPS） devices.The applicability of WMVFS to different weight factors,aggressive probabilities,densities of dynamic vehicles,and different two-route scenarios（symmetrical scenario and asymmetrical scenario with a speed limit bottleneck） is analyzed.Results show that WMVFS achieves the best performance compared with three other information feedback strategies when considering the traffic flux and stability.

Traffic dynamical characteristics and nonlinear density waves with consideration of navigation

In this dissertation, based on the existing macroscopic and microscopic models for traffic flow, several improved mathematical models in accordance with the rapid development of intelligent transportation system （ITS） are proposed, and the corresponding theoretical analysis and numerical simulation are performed. In addition, the relationships between macroscopic and microscopic traffic models are examined, in which emphasis is particularly laid on the investigation of the various nonlinear density waves in traffic flows. The contents of the dissertation are as follows.

随机车流对梁式桥模态参数识别的影响研究

现有的桥梁模态参数识别中,将随机车流视为一部分环境激励,忽略了车辆附加质量的影响,桥梁由于损伤导致的模态参数变化会被随机车流所引起的变化掩盖,从而影响后续损伤识别的正确性。文章利用元胞自动机模型模拟作用在桥梁上的随机车流的具体位置,将车流信息加入有限元模型,计算桥梁的动力响应;以简支梁和连续梁为例,应用随机子空间法识别模态参数,并比较车-桥系统、局部损伤桥梁和无损桥梁的模态参数差异;对比分析采用随机车流、单个移动车辆和静置车辆3种方式模拟车流时对频率与振型识别结果的影响。结果表明,桥梁局部损伤和随机车流均会导致识别的频率减小和振型改变,环境激励下的模态参数识别中必须考虑随机车流的作用并剔除其影响。

TWO-DIMENSIONAL MODEL OF TRAFFIC FLOW CONTAINING ROAD SECTIONS

Both the cross and road section are basic components in traffic systems. Ageneral cellular automaton model of two-dimensional traffic flow containing road section wasestablished. The model was simulated with respect to various section lengths and the randomdistribution of section lengths. The effect of road sections on the performance of traffic flow wasdiscussed based on simulation results

基于弹性安全换道间距的元胞自动机交通流模型

实际交通中,换道车辆的行驶速度不同,其所需要的安全换道间距也不尽相同。具体表是,高速行驶的车辆换道迅速、敏捷,而低速行驶车辆换道踌躇、犹豫。因而,对所有换道车均设定一个固定的安全换道间距是不恰当的,前人很少在这方面进行研究;结合现实提出的弹的安全换道间距规则,在改进前人模型仿真质量的同时,也提高了车辆的换道频率。模拟结果显示较以前模型,提出的元胞自动机模型将可改善道路的通行能力、提高道路资源的利用效率。

浓雾环境下车车通信对交通事故的影响分析

雾天环境下驾驶员会表现出和正常天气不同的驾驶行为,给行车安全带来威胁.为保证交通安全,交通管理部门在浓雾环境下关闭高速公路,给人们出行带来不便.分析浓雾环境下基于传统目视和基于车车通信的驾驶行为,建立了交通流元胞自动机模型.模拟结果表明:车车通信能够有效减少车辆分布的'局部聚集效应',从而大大降低交通事故率;当车辆密度较小时,交通事故率的降低效应尤其明显.本文的研究为高速公路在浓雾环境下采用车车通信技术实现车辆连续放行提供参考.

行人穿越马路对交通流的影响

结合交通心理学理论,在科学分析人为因素特征(如习惯性、随机性、从众心理等)的基础上,建立了行人乱穿马路行为的元胞自动机模型,数值模拟探讨了行人在一个位置和多个位置穿马路时交通运行状态与人为因素大小的参数之间的关系,重点研究了过街频率、过街位置分布、过街位置数目对交通流的影响.结果表明:基本图上存在饱和流量平台,其饱和流量值主要取决于行人过马路的时间和过街频率.在总穿越时间和总等待时间一定的情况下,穿越频率的提高扩大了饱和流量对应的密度范围,特别在高密度区,单次过马路时间的延长将显著降低道路的实际通行能力;过街位置是否均匀分布对交通几乎没影响;一般而言,相同条件下,让行人分散几处过马路要优于行人集中一处花费长时间过马路.

交通流中的自组织临界性研究

交通流元胞自动机模型呈现出显著的车流自组织临界性及从自由运动相到堵塞相的相变行为 .由于交通流模型中车辆之间的复杂耦合相互作用所引起的高阶时空关联 ,采用传统的考察局域格点车辆占据状态的动力学演化方法 ,尚未有任何国内外学者得到过高速车辆的一维和二维交通流模型的相变基本图的精确解析描述 .作者摒弃传统思路 ,采用以相邻车辆距离为变量的全局动力学演化考察方法 ,通过完全严格的逻辑推理及统计力学细致平衡条件的运用 ,首次给出了允许高速车随机减速的一维交通流 Fukui-Ishibashi元胞自动机模型相变基本图曲线的解析平均场方程 ,所得结果与模型的直接数值模拟可以精确地吻合 .基于交通流中实际车辆的加速及延迟行为 ,进一步提出两种新的一维交通流元胞自动机模型——限制加速模型和追尾车随机减速模型 .应用考察车距动力学演化的方法 ,仍然能够得到两个新模型相变基本图的精确解析平均场方程 .这些精确解析结果的获得既对于交通流复杂系统的自组织临界性和相变行为提供了基本的物理理解 ,又对于高速公路实际交通运输的信息管理和控制具有指导意义 .

基于元胞自动机交通流模型的车辆换道规则

将元胞自动机模型应用于周期性边界条件下的高速公路交通的换道规则模拟,并对不同条件下交通流的平均速度和流量进行仿真。基于驾驶员的性格差异,提出了更灵活的弹性换道规则,并探讨了不同换道规则对交通流流量等参数的影响。在计算机仿真过程中,通过变换交通流密度,得出了与不同换道规则对应的交通流基本图。结果表明:相对于以前的模型,遵循2种新规则的模型均可不同程度地改善道路的通行能力,提高道路资源的利用效能;从安全性角度进行对比分析,可得出较优的换道规则。

基于CA模型的中小学放学门口道路交通仿真

研究基于元胞自动机模型的中小学放学期间学校门口道路交通流仿真问题。在STNS(symmetric two-lane Nagel-Schreckenberg)模型的基础上,建立一个受中小学放学影响下学校门口道路交织区段的元胞自动机模型,对放学期间的道路交通流特性进行了仿真,对驾私家车接学生和乘校车学生比例、学校错峰放学对道路交通流的影响进行了仿真实验分析。结果表明减少私家车接学生比例、增加乘校车学生比例、选择合适的错峰放学时间,可在保证交通安全的前提下达到抑制交通拥堵、减少车辆总通行时间从而提高道路实际通行能力的目的,证明了该仿真模型的正确性。

一种考虑能见度影响的元胞自动机交通流模型

本文建立一种考虑能见度影响的元胞自动机交通流模型,研究了产生概率、消失概率及能见度对交通流的影响。计算机模拟结果表明,产生概率和消失概率均只在一定范围内影响系统流量的变化;能见度影响的路段为系统的瓶颈,为避免其上游路段出现严重堵塞,应根据能见度大小,对产生概率和消失概率进行合理调节;当能见度很低时,瓶颈路段及其上游路段出现严重堵塞。

转向概率对平面环行交叉路口交通流的影响

从道路结构出发,建立了具有内、外环道的平面环形交叉路口元胞自动机模型,研究了转向概率对平面环行交叉路口交通流的影响。计算机模拟结果表明,各车道的交通流在转向概率影响下呈现出不同的特点,转向概率均在一定的系统密度区域内对车道的交通流存在影响。

超速行为对交通流扰动影响的仿真研究

超速行驶是引起交通事故的主要原因之一,会造成巨大的人员与财产损失,基于元胞自动机对高速公路上的超速行为进行了研究。首先详尽分析了超速行驶特性,然后在现有的元胞自动机交通流模型基础上,构造了符合超速车辆特性的行驶规则,使之成为更符合现实道路状况的元胞自动机模型。该模型中的多种类型个体间交织影响,再现了现实交通流的非线性特点。运用新模型进行数值模拟仿真,发现超速行为将会降低交通流的平均速度,并且最终危害交通流的系统安全。