A cellular automaton model for a bridge traffic bottleneck

A cellular automaton （CA） model is proposed in this paper to analyze a bridge traffic bottleneck. The simulation results with this model show that there are several phase transitions in the traffic average density, velocity and flow for each lane under a periodic boundary condition. An unstable phase in the traffic average density and velocity for the upstream and downstream lanes of the bridge is shown in a range of initial traffic densities. The critical points of the phase transitions and the phenomenon of the unstable phase found in the simulation are also explained with the mean-field theory.

Identification and optimization of traffic bottleneck with signal timing

In urban transportation network, traffic congestion is likely to occur at traffic bottlenecks. The signal timing at intersections together with static properties of left-turn and straight-through lanes of roads are two significant factors causing traffic bottlenecks. A discrete-time model of traffic bottleneck is hence developed to analyze these two factors, and a bottleneck indicator is introduced to estimate the comprehensive bottleneck degree of individual road in regional transportation networks universally, the identification approaches are presented to identify traffic bottlenecks, bottleneck-free roads, and bottle- neck-prone roads. Based on above work, the optimization method applies ant colony algorithm with ef- fective green time as decision variables to find out an optimal coordinated signal timing plan for a re- gional network. In addition, a real experimental transportation network is chosen to verify the valida- tion of bottleneck identification. The bottleneck identification approaches can explain the features of oc- currence and dissipation of traffic congestion in a certain extent, and the bottleneck optimization meth- od provides a new way to coordinate signal timing at intersections to mitigate traffic congestion.

The effect of moving bottlenecks on a two-lane traffic flow

In this paper, we study the effect of moving bottlenecks on traffic flow. The full velocity difference （FVD） model is extended to the traffic flow on a two-lane highway, and new lane changing rule is proposed to reproduce the vehicular lane changing behavior. Using this model, we derive the fundamental current-density diagrams for the traffic flow with the effect of moving bottleneck. Moreover, typical time-space diagram for a two-lane highway shows the formation and dissipation of a moving bottleneck. Results demonstrate that the effect of moving bottleneck enlarges with the increase of traffic density, but the effect can be reduced by increasing the maximum velocity of heavy truck. The effects of multiple moving bottlenecks under different conditions are investigated. The effect becomes more remarkable when the coupling effect of multiple moving bottlenecks occurs.

Traffic Congestion Mechanism in Two Ramp Systems

The aim of this paper is to study traffic properties in an on/off-ramp system with a bus stop close to the on/off ramp. The location of the bus stop in the on/off-ramp （thereafter downstream or upstream case） is discussed. The simulation results show that in the two ramp systems, the reasons for traffic congestions are different. In the on-ramp system, buses and cars coming from on-ramp interweave each other, while in the off-ramp system, buses interweave with cars exiting to off-ramp. Thus, in the on-ramp （off-ramp） system, the upstream （downstream） bus stop is helpful to reduce the interweaving situation. Moreover, the negative effect will disappear when the distance between the bus stop and the on/off-ramp is more than 20 cells （i.e. 150 m）. These qualitative findings may provide some suggestions on traffic management and optimization.

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.

Evaluation of Merge Control Strategies at Interstate Work Zones under Peak and Off-Peak Traffic Conditions

Maintenance and rehabilitation projects of interstate facilities typically mandate lane closures. Lane closures require merging maneuvers that often result in reduced speeds and traffic bottlenecks. Work zone impacts on traffic operations are magnified when project durations are extended. Conventionally, work zone traffic control plans are developed to address work zone impacts. This study evaluated various merge control strategies at interstate work zones peak and off-peak traffic conditions and summarized related impacts. A comprehensive microscopic simulation model was developed in full consideration of driver/vehicle behavior at work zones. The analysis of simulation results revealed that merge control strategies, when implemented during peak and off-peak conditions, can preserve the level of service and provide favorable mobility, safety, and environmental impacts. In addition, results indicate that transportation agencies’ practice of scheduling work zone activities during the off-peak may not be the most optimum approach. Overall, the findings of this study highlight the need for evaluation of work zone scheduling practices in full consideration of agency, user, and project costs.

Bottleneck Merge Control Strategies for Work Zones: Available Options and Current Practices

Maintenance and rehabilitation projects of interstate facilities typically mandate lane closures. Lane closures require merging maneuvers that often result in reduced speeds and traffic bottlenecks. Conventionally, bottleneck merge control plans are developed to address bottlenecks impacts. However, there is a need to better understand the various merge control options and their potential impacts on traffic operations and safety. This study reviewed available options and current practices of bottleneck merge control strategies at work zones, and summarized transportation agencies’ considerations to mitigate adverse impacts. An extensive literature review was performed and a questionnaire survey was developed and used to gather relevant information. Input was solicited from all US State Departments of Transportation. Responses from 27 States revealed that transportation agencies currently rely on experience when selecting a bottleneck merge control strategy and often do not consider influence on construction activities. Thus, a gap was identified between bottleneck merge control and construction plans. Another gap was identified regarding the lack of formal criteria or guidelines for selecting a bottleneck merge control strategy. These gaps need to be addressed through investigating the influence of bottleneck merge control strategies on construction activities, and the development of formal criteria for effective selection of such strategies.

西安市幸福路跨陇海铁路总体方案研究

随着城市发展以及对中心区域的提质优化,那些在中心城区中存在的特别难以优化提升且制约因素较多的断头路,近些年来越来越引起相关职能部门及领导的重视。本文通过对交通瓶颈区域的建设空间进行调查,分析总结了通道限制因素,以提高区域交通效率、均衡路网流量、增强交通服务功能等为目标,通过系统性地对交通状况进行分析,优化立交节点方案,强化通道的可实施性,以期为今后类似通道项目设计提供技术参考。

考虑出行者到达时间无差异带的瓶颈模型

为了弥补Vickrey瓶颈模型及其拓展研究忽视了出行者有限理性特征的缺陷,从而降低瓶颈模型的误差,缓解城市交通拥堵,将通勤者有限理性的时间认识与瓶颈模型相结合。基于出行者对到达时间的感知存在无差异带的假设,建立了考虑出行者到达时间无差异带不对称的瓶颈模型,并对模型进行了出发率分析和均衡解分析。采用数值分析的方法详细推导了均衡出发率、总成本、均衡成本、最大排队长度、全部排队成本等指标。进一步地,将上述新建立的模型扩展到无差异带对称、早到时间无差异带、晚到时间无差异带情形下,同样进行了出发率分析和均衡解分析。通过与基本瓶颈模型相比较,分析了考虑无差异带不对称和3种扩展情形的瓶颈模型中,出行者的出发时间决策和均衡解的性质,最后利用数值算例对结论进行了验证。结果表明:在考虑出行者到达时间无差异带的条件下,总成本、均衡成本、总早到成本、总晚到成本、最大排队长度等指标均变小,而变小的幅度与早到、晚到无差异带的宽度之和有关;通勤者的出发率函数由2段变为3段;通勤高峰期或提前或推迟具体时间由单位早到时间成本、单位晚到时间成本、无差异带的宽度等参数值决定;采用弹性工作制,对应于考虑出行者到达时间无差异带不对称的瓶颈模型,能够均匀高峰期的车流量,从而减少拥堵。

杨高路改建工程浦建路跨线桥节点出入口匝道布置方案研究

自《上海市城市总体规划(2017-2035年)》发布以来,上海的城市建设从快速发展向精细化治理、综合性改造的建设思路转变。以浦东新区杨高路(世纪大道-浦建路)道路改造工程为背景,工程实施完工后,根据实际的道路运营情况,分析交通瓶颈的起因,结合交通需求,研究增设匝道出入口布置方案,在保证杨高路复合型走廊功能的基础上,在有限的空间里实现功能的最大化,解决交通瓶颈问题。

面向高速公路连续瓶颈的协同可变限速控制

高速公路瓶颈处极易因通行能力受限而诱发交通拥堵,进而导致通勤时间延长、燃料消耗增加、驾驶舒适性降低,尤其是在连续多瓶颈处,更容易对道路网络造成连锁反应而大范围增加事故风险。既有拥堵控制策略聚焦于孤立瓶颈处拥堵消除,通过对多个瓶颈路段实施多个孤立瓶颈控制策略,由于控制策略间交通状态与控制参数缺乏协同,致使控制效果受限,且极易因策略协同失衡导致更为复杂的交通拥堵。本文提出一种基于模型预测控制方法的连续多瓶颈拥堵消除的协同可变限速控制策略:首先,针对连续多瓶颈主动管控场景改进元胞传输模型,以模拟高速公路多瓶颈生成、通行能力下降、随机交通流波动和可变限速控制状态与效果;其次,基于拉格朗日坐标系改进LWR模型,以精准预测交通拥堵场景下的交通流随机状态;再次,构建以多瓶颈路段总体交通运行状态作为输入的可变限速控制策略,并采用反馈式控制框架协同多瓶颈可变限速控制策略;最后,通过构建仿真实验测试了所提出控制策略消除连续瓶颈处拥堵的控制效率,并与其他控制策略进行了效果对比。实验结果表明,本文所提出的协同可变限速策略可有效消除连续瓶颈的多处拥堵,且控制效果显著优于其他控制策略,车辆总行程时间和总延误时间分别降低21.3%和70.6%。

W基于家庭通勤行为分析的共享停车优化研究

共享停车是缓解早高峰城市中心区域车位紧张的有效手段。基于瓶颈理论构建汇流瓶颈路网下个人与家庭混合出行的均衡出行模型,考虑共享停车影响下的出行行为决策,在多停车场条件下分析家庭与个人的通勤行为,比较通学通勤时间差的不同对各类出行者的出行时间及出行成本的影响,并基于均衡模型对共享停车规模进行优化,分析交易成本对出行行为选择的影响。研究发现:在多停车位竞争的情况下,用户会产生更多的早到成本,当通学通勤时间差较大时可以延缓系统高峰期,扩大共享车位规模可以达到对系统的优化。故政府应合理设置通学通勤时间差,在考虑社会总成本的情况下制定相关政策对共享停车规模进行优化,对共享交易成本进行管理从而实现资源的合理利用。

考虑自动驾驶专用道和组合管理策略的通勤行为建模及分析

考虑自动驾驶背景下新型多模式通勤方式并存的情景,设置存在自动驾驶汽车专用道,即传统汽车与自动驾驶汽车分离出行的双车道交通系统,基于瓶颈模型进行建模,分析实施可交易电子路票与鼓励合乘组合管理策略前后对路票市场价格、通勤者出行方式选择和自动驾驶汽车内生渗透率的影响,并以系统总成本改善效果最佳为目标,协同优化组合管理策略参数。研究表明:实施组合管理策略后,路票市场价格可唯一确定;部分独驾通勤者转向合乘出行,系统总车辆数减少,两车道的早高峰持续时间均缩短,交通拥堵得到改善;存在满足特定关系的组合管理策略参数使得系统总成本改善最佳,且能够得到系统最优时的私人自动驾驶汽车和共享自动驾驶汽车的市场渗透率。研究可为未来城市交通管理提供新的思路。

基于改进YOLOv5算法的道路交通参与者实时检测方法

从道路监控图像中快速准确地检测交通参与者对于智能交通系统监管道路目标具有重要意义。为解决传统YOLOv5目标检测算法对多种交通参与者目标检测精度低、重叠目标漏检等问题,研究了基于改进YOLOv5算法的道路交通参与者实时检测方法。为增强浅层网络提取图像特征信息能力,采用融合移动翻转瓶颈卷积(FusedMBC)代替原卷积结构,并通过自注意力机制学习交通参与者的纹理特征;为加强主干网络感知图像空间特征信息的能力,引入坐标注意力机制(CA),使主干网络更加关注图像中交通参与者的语义特征;为使普通卷积拥有感知构造能力,以增强激活空间的灵敏度,采用漏斗激活函数(FReLU)作为卷积层的激活函数,并能够使特征向量进行像素级建模;为增强网络对密集目标的空间特征信息提取能力,在特征融合网络中加入坐标注意力机制,通过注意力捕捉密集目标融合后的空间与通道特征信息,让网络精确定位各个目标。通过对车路协同自动驾驶数据集DAIR-V2X的交通参与者图像进行数据增强预处理,构建用于验证模型性能的测试集2000张并进行了算法验证。实验结果表明:①改进后的YOLOv5算法平均检测精度达到82.4%,平均召回率达到95%,平均检测速度达到204帧/s。②相比于原始YOLOv5,其在平均检测精度和平均检测速度分别提高了5.8%和33.3%,证实提出的方法能够实现快速准确地检测交通参与者,有助于提升智能交通系统监管交通参与者的能力。

交通瓶颈下相序设置对路口交通状况影响分析

针对路段发生交通瓶颈时上游路段可能出现的溢流现象,在分析不同相序设置下进入交通瓶颈路段车流构成的基础上,应用车流波动理论,从进入交通瓶颈路段的车流与交通瓶颈通行能力间关系出发,分别就不同相序相同车流量以及相同相序不同车流量时交通瓶颈上游车流的集散波进行分析对比,将周期内不同的相序设置及车流量对交通瓶颈上游溢流情况的影响进行了研究,针对各种情况,得到通过改变相序避免溢流情况发生需要满足的条件。研究结果表明,在某些条件下,相序的变化对避免溢流现象发生的影响不大,而当满足一定条件时,通过改变相序设置可以有效的避免溢流情况的发生。

采用交通出行量数据的多点联动瓶颈控制方法

为了精确定位瓶颈路段的需求来源、均衡瓶颈路段交通需求时空分布,防止溢流及拥堵转移,提出基于视频信息提取的交通出行量(OD)数据的搜索诱发路段瓶颈的关键车流路径与可控制路段方法,确定瓶颈调控节点;以上游区域为控制对象、以特定时间内消散路段瓶颈为控制目标,估算驶入流量总调节量,并基于路段的剩余容量建立调节量在可控制路段之间的分配方法,优化控制节点的信号方案.以贵阳市的实际数据为例,瓶颈触发使用滚动时间占有率为指标,采用VISSIM仿真软件,结果表明:与采用常规控制方案相比,采用新方案时最大排队长度降低了31.39%,区域车均延误降低了26.00%.

基于检测线圈数据的道路交通瓶颈分析

为向交通管理、道路改造、交通出行等提供服务,以定点检测线圈数据为基础,根据交通参数关系拟合后得到拥挤阈值,对交通参数时空变化图进行瓶颈位置识别,再使用"变形累计曲线法"进一步研究瓶颈附近交通拥挤特征。此外,文章对"变形累计曲线法"中关键问题进行了讨论,得到了曲线变化所揭示的意义和背景参数值的确定方法。以上海市南北高架东侧部分路段为例,对早上6∶00—12∶30瓶颈附近路段的拥挤状况进行了分析,确定了瓶颈位置并得到了瓶颈处拥挤的开始时间、结束时间和拥挤持续时间。

基于时空检测的城市交通网络瓶颈识别方法研究

为了解决拥堵状态下交通网络瓶颈识别问题,文章基于时空检测数据对道路节点和路段拥堵状态进行了分析,并以此为基础建立了城市交通网络瓶颈识别与分类模型。拥堵发生期间,以任意2辆浮动车连续通过拥堵路径各个交叉口时间间隔作为统计时间,以拥堵路径各个交叉口对应流向流出率作为统计对象,连续统计多辆浮动车通过时的交通量序列,建立了拥堵路径交叉口关联度模型并以此划分交通网络瓶颈。以划分的交通拥堵瓶颈区域作为密闭区域,通过分析拥堵路径平峰期间与拥堵期间的流入流出率,使用切比雪夫不等式在置信度95%范围内建立了拥堵瓶颈的3类模型:输入型瓶颈、输出型瓶颈和通过型瓶颈。以实际区域道路网络为研究对象,使用上述模型对拥堵区域进行了分析,结果表明该模型可有效识别并分类交通网络瓶颈。

基于均衡原理的单向交通瓶颈路段诊断法

以单向交通组织区域边界的道路节点为OD点,把交叉口转向流线虚拟成路段,转向车道的通行能力作为虚拟路段的容量,转向车道的行程延误作为虚拟路段的交通阻抗,与实际的路段一起组成单向交通组织区域节点OD之间的路径,采用集合运算合成节点OD之间的通道容量。利用交通均衡方法,经交通分配得到单向交通组织区域的路段和虚拟路段的交通量。通过计算饱和度判断路段和交叉口的拥挤程度,诊断出交通瓶颈,为单向交通组织方案的完善提供可靠的支持。

信息化条件下交通拥堵瓶颈识别与扩散判别

为了有效地甄别网络交通拥堵瓶颈、改善交通运行状况和预防交通拥堵扩散,考虑交通信息的影响效用,构建了基于路径选择行为的网络交通拥堵扩散模型,该模型包含描述交通流在路段上扩散的交通分配模型和表征交通信息对路段交通流影响的路径选择行为模型两部分,以Nguyen-Dupius经典网络为例,模拟仿真了不同交通需求水平下网络交通拥堵瓶颈扩散与识别,并对比分析有无信息提供条件下交通拥堵扩散规律.结果表明,交通需求水平连续增长是诱发交通拥堵的最直接因素;交通拥堵瓶颈形成与扩散不仅取决于路段在网络上所处位置和交通需求,还取决于交通信息提供与否;但是交通信息的提供在某种程度上可以改善当前交通状况.