Perimeter traffic control strategy based on macroscopic fundamental diagrams

A perimeter traffic signal control strategy is proposed based on the macroscopic fundamental diagram theory(MFD)to solve the signal control problem in oversaturated states.First,the MFD of a specific regional network can be derived using VSS IM simulation software.Secondly,the maximum number of cumulative vehicles that the network can accommodate is determined based on the MFD.Then,through monitoring the influx flow,the number of vehicles existing in and exiting from the network,a perimeter traffic control model is proposed to optimize the signal timing of the boundary intersections.Finally,a virtual network simulation model is established and three different kinds o f traffic demand are loaded into the network.Simulation results show that a fer the strategy implementation,the number o f vehicles accumulating in the network can be kept near the optimal value,while the number o f both entering and exiting vehicles increases significantly and the road network can be maintained at a large capacity.Simultaneously,the queue length at the approach of the border intersections is reasonably controlled and vehicles entering and exiting the network can maintain a more efficient and stable speed.The network performance indices such as the average traffic delay and average number of stops can be improved to a certain degree,thus verifying the effectiveness and feasibility of the perimeter control strategy.

Quantification of the Hysteresis of Macroscopic Fundamental Diagrams and Its Relationship with the Congestion Heterogeneity and Performance of a Multimodal Network

Recent studies have observed hysteresis loops in the macroscopic fundamental diagram (MFD). In particular, for the same network density, higher network flows occur during congestion onset than during congestion offset. To evaluate management strategies using the MFD, investigating the relationship between the size of these loops and network performance is needed. The existing literature has mainly discussed correlating loop width (difference in density) and height (capacity drop) with congestion heterogeneity, but has failed to prove a relationship between the capacity drop and traffic conditions. Moreover, quantification of the MFD loop in complex multimodal networks has not been investigated. The objective of this paper covers these aspects. We simulated the Sioux Falls network with different mode-share ratios (car and bus users) based on a multi-agent simulation, MATSim. We investigated the relationships between MFD loop size and congestion heterogeneity (standard deviation of density) and network performance (average passenger travel time), and found that both were directly correlated with loop width, while weakly correlated with loop height. Moreover, we divided the MFD loop into two parts according to congestion onset and offset periods and found that the heights of the two parts had opposite effects. Accordingly, we show why the relationship between capacity drop and congestion heterogeneity is not found in the literature. We also found that network performance inversely affected the height of part of the loop while the height of its other part increased with an increase in congestion heterogeneity. These results help to evaluate network performance in the presence of MFD hysteresis, leading to elaborated management decisions.

Study of macroscopic fundamental diagram on Shanghai urban expressway network in China

The macroscopic fundamental diagram（ MFD） is studied to obtain the aggregate behavior of traffic in cities. This paper investigates the existence and the characteristics of different types of daily MFD for the Shanghai urban expressway network. The existence of MFD in the Shanghai urban expressway network is proved based on two weeks＇ data.Moreover, the hysteresis phenomena is present in most days and the network exhibits different hysteresis loops under different traffic situations. The relationship between the hysteresis phenomena and the inhomogeneity of traffic distribution is verified. The MFDs in the years of 2009 and 2012 are compared. The hysteresis loop still exists in 2012, which further verifies the existence of the hysteresis phenomenon. The direct relationship between the length of the hysteresis loop（ ΔO） and the congestion is proved based on sufficient data. The width of the hysteresis loop, i. e., the drop in network flow（ ΔQ） has no relationship with the congestion, and it varies from day to day under different traffic situations.

Vehicle emissions calculation for urban roads based on the Macroscopic Fundamental Diagram method and real-time traffic information

Vehicle emissions calculation methods mostly use ownership information or annual road monitoring data as the activity level to calculate air pollutant emissions,but it is hard to reflect either the emissions intensity under different conditions or the spatiotemporal characteristics in various sections based on such approaches.This paper presents a method based on the Macroscopic Fundamental Diagram and real-time traffic data to calculate vehicle emissions,which could reflect the operation conditions and emission characteristics of vehicles.Following the‘Technical Guide for the Compiling of Road Vehicle Air Pollutant Emissions Inventories’,the emissions of three roads with different lane numbers and road grades in Beijing were estimated and verified using this method.Compared with monitoring data,the average deviations of the traffic flow on the Fifth Expressway,Jingfu National Highway,and Jingzhou Provincial Highway were?25.5%,?26.5%,and?13.4%,respectively,and the average deviations of nitrogen oxides emissions were?27.7%,?12.9%,and?12%,respectively.This method showed good application potentials to construct the emissions inventory applied to the block-scale model and analyze the spatiotemporal distribution characteristics of motor vehicle emissions in urban areas.

基于MFD的快速路新型混合交通流特性分析

为探究智能网联车辆(CAV)与人工驾驶车辆混行情况下快速路的宏观交通流特性,研究了CAV渗透率对快速路宏观基本图(MFD)的影响规律.首先,利用MFD临界点和拥堵拐点的特征属性,构建考虑CAV渗透率的MFD分段拟合模型;其次,从拥堵持续时间、拥堵严重程度和MFD迟滞现象3个方面分析CAV渗透率对快速路拥堵过程的影响;最后,采用SUMO搭建仿真环境,对提出方法进行验证.结果表明:提出的分段拟合方法在拟合优度及跟踪MFD临界点上均优于三次拟合方法;CAV的引入并不会消除快速路MFD的迟滞现象,但其持续时间会随着CAV渗透率的增加而降低;快速路拥堵严重程度随CAV渗透的增大而降低,当CAV渗透率超过0.5时,拥堵的改善效果开始减弱.

Bus frequency optimization in a large-scale multi-modal transportation system:integrating 3D-MFD and dynamic traffic assignment

A properly designed public transport system is expected to improve traffic efficiency.A high-frequency bus service would decrease the waiting time for passengers,but the interaction between buses and cars might result in more serious congestion.On the other hand,a low-frequency bus service would increase the waiting time for passengers and would not reduce the use of private cars.It is important to strike a balance between high and low frequencies in order to minimize the total delays for all road users.It is critical to formulate the impacts of bus frequency on congestion dynamics and mode choices.However,as far as the authors know,most proposed bus frequency optimization formulations are based on static demand and the Bureau of Public Roads function,and do not properly consider the congestion dynamics and their impacts on mode choices.To fill this gap,this paper proposes a bi-level optimization model.A three-dimensional Macroscopic Fundamental Diagram based modeling approach is developed to capture the bi-modal congestion dynamics.A variational inequality model for the user equilibrium in mode choices is presented and solved using a double projection algorithm.A surrogate model-based algorithm is used to solve the bi-level programming problem.

不同降雨量下基于宏观基本图的边界控制策略

在雨雪等不利天气条件下,城市交通拥堵加剧,北京、天津等大城市在降雨条件下经常发生多路段区域性交通拥堵。因此,根据天津市中心城区和市郊区域路网实际交通数据,以路网交通流宏观基本图模型为研究基础,对比不同降雨量以及不同路网的路网交通流时序和宏观基本图变化规律,分析不同降雨量对天津市中心城区和市郊区域路网交通状态的影响。基于不同降雨量下中心城区和市郊区域路网宏观交通流的变化规律,分别构建路网动态演化模型,并对模型的参数进行标定和有效性验证。针对降雨条件下路网发生的区域性拥堵问题,基于宏观基本图的边界控制分别设计了不同降雨量下中心城区和市郊区域路网控制策略,通过仿真实验分析验证了不同控制策略的效果,并给出了能够缓解中心城区和市郊区域路网拥堵的可行策略。结果表明:在小雨天气条件下,将从市郊区域向中心城区的交通流量的转移比例减小量控制在9%~50%范围之内时,中心城区与市郊区域交通状态更加均衡,路网调控效果更好;在大雨天气条件下,将从市郊区域向中心城区的交通流量的转移比例减小量控制在23%~50%范围之内时,中心城区与市郊区域交通状态更加均衡,路网调控效果更好。这表明该控制策略能够缓解中心城区和市郊区域路网的交通拥堵,保障路网交通系统的稳定运行。

多个MFD子区边界协调控制方法

为了改善交通网络运行状况,根据车流密度的差异对宏观路网进行子区划分,提出了面向多个宏观基本图(Macroscopic fundamental diagram,MFD)子区的边界协调控制方法.根据划分的多个子区间邻接关系和流入流出交通流率,建立了路网车流平衡方程.通过与最佳累积车辆数进行比较,确定了拥挤度高的子区边界交叉口最佳流入与流出的交通流量;进而建立了以整个路网旅行完成流率最大、平均行程时间和平均延误最小的多目标边界协调优化模型,并通过自适应遗传算法对多目标函数进行求解.以存在4个MFD子区的实际路网为分析对象,对比仿真结果表明所提方法可有效提高路网运行效率、缓解拥堵状况.

基于MFD的城市区域过饱和交通信号优化控制

为了解决交通高峰时段城市区域路网过大的交通需求引起的路网通行效率下降以及区域内部交通流分布的异质性产生的道路资源浪费等问题.本文提出了基于区域路网固有属性宏观基本图(Macroscopic fundamental diagram,MFD)的过饱和区域控制优化模型,建立了边界控制信号和内部控制信号目标函数的双层规划优化,进一步设计了基于BP(Back propagation)神经网络的自适应动态规划(Adaptive dynamic programming,ADP)模型,对建立的双层规划区域交通信号进行求解,实例仿真结果验证了本文方法的有效性.通过本文的研究分析,对城市区域交通的需求管控、拥堵政策制定等城市区域交通管理具有一定的指导意义.

基于MFD的路网宏观交通状态及影响因素研究

从城市路网交通管理与控制的需求出发,引入交通流宏观基本图(MFD)模型,基于实测和仿真数据,开展对北京市西三环实际路网的宏观交通状态、时变特征以及影响因素研究.文中首先介绍了MFD模型及其矢量算法,利用实测数据建立西三环路网的MFD,基于Van Aerde模型标定路网交通流特征参数,对比分析路网平均流量-平均密度关系的时段分布差异,并得到宏观交通流的"磁滞现象";其次,证明了交通密度分布的不均衡性是影响路网宏观交通状态的根本因素;最后,利用Integration仿真研究了路网结构、交通需求以及出行路径对路网车流密度分布、宏观交通状态及其变化趋势的影响,以期为宏观交通控制、拥堵治理措施的制定提供决策支持.

基于MFD的城市区域路网多子区协调控制策略

针对城市路网中区域性的大范围交通拥堵问题,提出了基于宏观基本图(Macroscopic Fundamental Diagram,MFD)的多子区协调控制策略,以提升路网的整体运行效益.该策略将城市区域路网划分为多个子区,每个子区的交通流又划分为内部流和转移流,综合两者建立了基于MFD的多子区交通流模型,并给出了对各子区交通流诱导时的边界约束条件;通过调节子区边界控制输入,设计了边界反馈控制器对各子区转移流进行动态诱导,继而进行了迭代分析,以判断其是否满足边界约束,并对控制器进行了Lyapunov稳定性分析.仿真结果表明,所提策略使城市区域路网中各子区车辆总数渐近收敛于设定值,且整体平均流量提高了约11%,大范围交通拥堵状况得到明显缓解.

基于地面路网MFD的快速路出口匝道流量分配模型

过于集中的流量分配易导致出口匝道和与之相衔接的地面道路过饱和,进而影响快速路和地面路网的通行效率.为提高路网中车辆通过快速路到达目的地的通行效率,基于地面路网宏观基本图(Macroscopic Fundamental Diagram,MFD),以出口匝道通行能力和与之相衔接的地面路网承载能力为约束条件,以整个路网的车辆总行程时间最短为优化目标,建立快速路出口匝道流量分配模型.根据宏观网络车流平衡方程,采用改进的遗传算法对模型进行求解.最后,通过实际路网验证了模型的有效性.结果表明,该模型可有效提高车辆通过快速路到达目的地的通行效率,同时降低出行成本.

基于MFD的路网理论效能最优交通指数计算方法--以北京市为例

针对交通运行指数(Traffic Performance Index,TPI)合理值取值问题,将宏观基本图(Mac⁃roscopic Fundamental Diagram,MFD)模型与交通运行指数模型相结合,提出理论效能最优交通指数的求解方法.首先,利用各等级道路交通流基本图模型,建立全路网MFD,寻找路网理论效能最优状态点;其次,以速度为连接,将该点映射至基于严重拥堵里程比的交通运行指数模型中,得到理论效能最优交通指数;最后,以北京市全路网及行政区为例进行实证研究.结果表明:全路网的理论效能最优交通指数为6.42,东城区、西城区、海淀区和朝阳区理论效能最优交通指数依次为6.86,6.80,6.76,4.58.朝阳区理论效能最优交通指数最低,其路网性能优于其他三区.该方法为交通管理和交通出行提供直观参考,并为制定交通管理政策提供理论支撑.

基于MFD的路网边界控制策略研究综述

网络交通流宏观基本图是路网的固有属性,可以从宏观层面监测路网运行状态,故近年来,MFD在网络控制领域中得到广泛应用。本文对基于MFD的路网边界控制策略相关研究成果进行了回顾,分析总结了目前针对单一网络和多个子区的边界流量控制策略方面所取得的成果,并梳理出具有研究价值的方向和问题,在交通拥挤日益严重的背景下,成果可以提升网络边界控制策略在缓解交通拥挤应用上的有效性,从而增强路网整体运行效益。

考虑干扰的交通子区模糊迭代学习边界控制

针对固定增益迭代学习控制器跟踪交通子区内期望累计车辆数n^(*)的速度较慢,迭代次数过多的问题,并考虑到实际交通子区内存在的干扰对其运行状态的影响,建立了含有干扰项的交通流模型并对其进行离散化。采用开闭环比例微分(proportion differentiation,PD)型模糊迭代学习控制器,根据研究子区实际路网内的累计车辆数与期望累计车辆数n^(*)的误差及其变化率对开闭环PD型迭代学习控制器的迭代学习增益和反馈增益进行调整,使交通子区内的实际累计车辆数可以较快速地跟踪期望累计车辆数n^(*),并对开闭环PD型模糊迭代学习控制器的收敛性进行严格证明。通过对轻度和中度干扰影响下的交通子区进行仿真,结果显示,对比固定增益迭代学习控制器,开闭环PD型模糊迭代学习控制器的误差收敛速度分别提高24%和31%,平均排队长度分别减少24.52%和16.55%,平均延误分别减少21.63%和19.23%,平均停车次数分别减少23.68%和10.77%。

基于MFD的高铁站周围路网诱导-控制方法

区域边界控制在缓解城市区域交通拥堵方面具有巨大的潜力,但同时容易导致区域边界处形成严重的排队现象。为了解决这一问题,结合高铁站周围路网的交通特性,提出了一种将交通诱导与区域边界控制相结合的基于宏观基本图(Macroscopic Fundamental Diagrams,MFD)的诱导-控制方法。首先,为满足同质性要求,划分路网子区,建立各子区的宏观交通流平衡方程,确定每个子区最佳的车辆数积累;其次,根据各子区的交通状态,实时更新诱导-控制措施,在优先使用交通诱导方式的前提下对高铁站周围路网的交通流进行动态管控;最后,以西安北站周围路网为分析对象,通过仿真分析,对比了无区域边界控制、单一边界控制和诱导-控制三种情况下的管控效果。结果表明,在诱导-控制条件下,区域的平均车速较其他两种情况下分别提高了25.39%和4.61%,平均车辆延误分别减少了28.22%和10.05%,尤其是车辆在落客区的延误明显减少。基于MFD的诱导-控制方法可有效缓解高峰客流时段高铁站周围路网的拥堵,提高客流和车流在高铁站的集散效率。

基于三维宏观基本图的城市机非混行交通研究

为解决城市交通中机动车与非机动车混合行驶造成的交通拥堵,提出一种三维宏观基本图的理论分析方法,探究机动车与非机动车混行交通流的微观运行特征和宏观演化规律,揭示在非机动车干扰下交通拥堵的形成、传播和消散机理。先分别建立描述非机动车流的元胞自动机模型和机动车流的元胞传输模型,并借助非机动车越线次数函数将两个模型耦合;然后,在Simulink仿真平台上,运行该耦合模型以求得路网的三维宏观基本图,并以此分析非机动车驶入流量与路网平均流量、冲突次数三者间的相互关系;最后,提出提高路网硬隔离占比和加大非机动车道宽度的两种方法,借助三维宏观基本图来验证其缓解交通拥堵的效果。研究结果表明:三维宏观基本图的分析方法可量化机动车和非机动车冲突的影响,指导混行交通拥堵的治理,该结论为改善中国城市交通出行秩序和出行环境提供了参考。

基于PID控制的交通边界控制方法

随着城市化进程的不断加速,交通拥堵已成为城市面临的主要挑战之一。为了解决城市路网中心区域因车辆累积而导致的拥堵问题,本文利用宏观基本图的特有属性,提出了基于PID控制的交通边界控制方法。首先,建立被控区域车辆动态平衡方程,确定被控区域与外部区域车辆转移关系;其次,引入PID控制器作为路网边界控制器,通过调节进入被控区域的车辆转移比率,控制进入被控区域内部的车辆数;最后,利用VISSIM仿真软件的仿真结果表明:路网内部的车辆总数能够稳定在最佳累积值附近。

基于MFD的边界控制方法仿真分析

路网交通流宏观基本图(MFD)是用于描述路网交通流宏观变量(流量、密度、速度)间的关系模型,城市路网交通流MFD的提出与发现对于城市路网交通流运行状态评价与控制具有重要的理论意义与应用价值。本文将比例-积分控制策略应用于北京望京地区路网中,并比较了不同情况下路网运行指标的差异。

基于MFD的城市路网运行状态分析及关键路段辨识——以青岛市为例

宏观基本图(MFD)是刻画路网平均流量和平均密度的关系模型,对路网运行状态分析、出行者路径选择和宏观交通控制有重要的作用。以青岛市台东商圈交通流检测器数据为基础,分析城市路网运行状态,并提出一种基于MFD的关键路段辨识的重要度指标,进一步识别路网中的关键路段。结果表明:青岛市台东商圈路网宏观基本图存在"磁滞现象",且在时间序列上呈现"M"状分布;据对其工作日、周末和节假日的宏观基本图分析,发现不同时段的路网运行状态存在差异;在关键路段的识别中,采用了MFD对比与重要度指标测算相结合的方法,验证了指标模型的合理性和准确性。