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.

Development of control strategy of variable speed limits for improving traffic operations at freeway bottlenecks

A control strategy of variable speed limits(VSL)was developed to reduce the travel time at freeway recurrent bottleneck areas.The proposed control strategy particularly focused on preventing the capacity drop and increasing the discharge flow.A cell transmission model(CTM)was developed to evaluate the effects of the proposed VSL control strategy on the traffic operations.The results show that the total travel time is reduced by 25.5% and the delay is reduced by 56.1%.The average travel speed is increased by 34.3% and the queue length is reduced by 31.0%.The traffic operation is improved by the proposed VSL control strategy.The way to use the proposed VSL control strategy in different types of freeway bottlenecks was also discussed by considering different traffic flow characteristics.It is concluded that the VSL control strategy is effective for merge bottlenecks but is less effective for diverge bottlenecks.

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。

Traffic Congestion Mechanism in Two Ramp Systems

这份报纸的目的离开／关斜面与一个汽车站在一个 on/off-ramp 系统学习交通性质靠近。在 on/off-ramp (此后下游或在上游的案例) 的汽车站的地点被讨论。模拟结果证明在二个斜面系统，为交通拥挤的原因是不同的。在在斜面上系统，，来自在斜面上的公共汽车和汽车在离开斜面系统交织对方，公共汽车交织，汽车退出到离开斜面。因此，在在斜面上(离开斜面) 系统，在上游(下游) 汽车站是有用的减少交织的状况。而且，当在汽车站之间的距离和 on/off-ramp 是超过 20 个房间时，否定效果将消失(即 150 m ) 。这些质的调查结果可以在交通管理和优化上提供一些建议。

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.

Properties of Bottleneck on Complex Networks

交通瓶颈在大多数自然、人工的网络起一个关键作用。这里我们在场一简单地为瓶颈为动态特征考虑建模由考虑网络拓扑学特征和系统尺寸的复杂网络上的可靠性。我们发现有拥挤交通发生的网络交通免费却上面的流动在下面产生的批评的率。另外，随机的网络让更大的批评流动产生比放大免费的评价，这被发现。分析结果可能为设计网络实际上是有用的，特别为城市的交通网络。

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.

无人驾驶停车共乘缓解瓶颈拥堵研究

利用无人驾驶车辆利于共乘和自行停车的特点,提出了一种新的高效的通勤模式——无人驾驶停车共乘。首先,基于扩展的瓶颈模型,解析了该出行模式下瓶颈处通勤行为的均衡特征,建立了共乘率、停车收费与出行成本(包括瓶颈排队、工作延误、共乘隐私损失及共乘下车延误)之间的定量关系,给出了可诱导至系统最优的拥堵收费方案。然后,实施了数值实验,证明了模型的有效性,探究了模型中关键参数对出行费用的影响。最后,提供了该通勤模式可以应用的实际场景。解析和数值实验结果均表明,该通勤模式可缩短早高峰出行的持续时长,简化出行过程,从而大幅减少出行费用和换乘停车场规模,可为未来解决城市交通拥堵和市中心停车位缺乏等难题提供借鉴。

上海虹桥高铁站停车库交通组织与动态管理研究

超大型地下车库因其车位数量多、内部空间大,容易出现出入口处拥堵、内部绕行严重、双向寻车位低效等问题。以上海虹桥高铁站地下车库为研究案例,首先,分析虹桥站地下停车库的布局以及拥堵成因,并从理想交通运行角度,提出超大型停车库交通组织与动态管理的“无瓶颈、低损耗”的工作原则;其次,对照该原则,从流线设计、交通设施设置、日常管理等方面对虹桥站车库交通组织与动态管理问题进行剖析,并提出“去瓶颈、减损耗”的针对性改进措施。研究成果已在实践中得到应用。

高速公路连续瓶颈混合交通流可变限速与换道协同控制方法

为缓解高速公路连续瓶颈区车辆强制换道造成的通行能力下降的问题,减轻瓶颈之间的相互干扰,提出了面向智能网联车辆(connected and automated vehicles,CAVs)与普通车辆混行情况的高速公路连续瓶颈可变限速与换道协同控制策略。对传统的细胞传输模型(cell transmission model,CTM)进行改进,使其更好地预测考虑了可变限速地混合交通流状态;基于实验模拟,得到了不同交通需求场景下合理的换道控制段长度,通过对瓶颈上游车流进行预先换道提醒,缓解因强制换道引发的通行能力下降现象,进而提高可变限速控制的效果,同时利用可变限速对高交通需求下的流量进行调控,为换道控制段内车辆能够完成预先换道提供保障;构建了连续瓶颈下协同控制框架,并以最小化总行程时间和速度差为目标,优化连续瓶颈的交通运行性能;分析了3种CAVs渗透率对协同控制的影响。结果表明:相比于无控制和可变限速控制,在协同控制下总行程时间分别降低了54.76%和33.05%,总速度差分别减少了86.84%和29.58%。此外,CAVs对协同控制性能和道路运行状况有着积极作用。当CAVs渗透率为0.5时最低限速值由渗透率为0时的30 km/h提高至60 km/h,当渗透率为1时限速值始终保持在自由流速度,随着CAVs渗透率的增加协同控制下系统的总行程时间可从239.64 h减少至158.86 h。研究可为高速路连续瓶颈和未来含CAVs的混合交通流主动管控提供参考。

面向宽窄交替航道的船舶交通元胞自动机模型

为了提高宽窄交通航道的通行效率,针对宽窄交替的结构特点,以基尔运河为例,根据其航道宽窄段交替结构的特点,建立了双向船舶交通流元胞自动机模型,研究基尔运河的船舶交通流仿真。根据基尔运河的实际结构建立元胞空间,并基于固定闭塞理论和移动闭塞理论建立演化规则。基尔运河的结构导致大型船舶无法在狭窄的区间内同时通过,为了描述该现象,在元胞自动机模型中建立了合适的等待规则。在仿真分析中,主要讨论了不同船舶入流率、大小船舶比例、船舶间安全距离的影响。在仿真结果的基础上,进一步研究了基尔运河船舶交通流改善的瓶颈识别和改进策略。结果表明,基尔运河窄段长度过长是瓶颈所在,其使得运河内船舶大量停泊等待。

组合匝道瓶颈下交通流相变研究

针对组合匝道瓶颈附近发生的交通崩塌现象,提出了概率论主方程模型用以描述该现象。基于三相交通流理论,分析得出初始非均匀自由流中交通崩塌现象发生的本质是自由流到同步流的一阶相变,同时假设了一个确定性的局部扰动始终位于瓶颈附近,该扰动造成了过加速效应对于速度适应效应的竞争劣势。然后构建了合适的概率论主方程模型,并进一步推导得到了交通拥堵的平均迟滞时间和相变概率的表达式。理论结果的进一步分析表明:入口匝道流量的增加将加快交通流相变的进程,出口匝道流量对维持交通流的稳定性有促进作用,并且主干道流量对自由流波动影响较小,因此控制入口匝道流量的汇入对维持组合匝道瓶颈处初始自由流的稳定性非常重要。

高速公路改扩建工程周边路网交通瓶颈识别

为满足日益增加的交通需求和提高通行质量,同时保障高速公路区域路网和作业区的交通正常运行,有必要开展高速公路改扩建工程周边路网交通均衡诱导研究,对改扩建高速公路上过载的交通流量进行分流和转移。准确地识别高速公路周边路网的交通瓶颈路段,是进行高速公路改扩建工程周边路网交通均衡诱导的重要基础。在对国内某高速公路改扩建工程周边路网交通运行状况调研的基础上,耦合了速度-密度关系模型和服务水平法,构建了交通瓶颈识别模型。然后,基于所构建的交通瓶颈识别模型,结合周边路网的通行能力和不同时段的服务水平,对周边路网不同时段下的交通瓶颈路段进行识别。

基于深度强化学习的平滑车速控制系统

为调整不同路段的限速值,平滑交通流,从而提升高速公路车辆通行的安全性和效率,针对交通瓶颈区设计一种基于深度强化学习的平滑车速管控系统。该系统主要包含动态限速启动、限速值确定与更新和情报板动态发布等3个模块。将深度强化学习算法DDQN(Double Deep Q-Network)引入系统中,提出一种基于DDQN的平滑车速控制策略,从目标网络和经验回顾2个维度提升该算法的性能。基于元胞传输模型(Cellular Transmission Model,CTM)对宁夏高速公路某路段的交通流运行场景进行仿真,以车辆总通行时间和车流量为评价指标验证该系统的有效性,结果表明该系统能提高瓶颈区内拥堵路段车辆的通行效率。