The effects of group and position vacancy on pedestrian evacuation flow model

In order to reduce the simulation error of pedestrian evacuation model, a novel three-dimensional cellular automata model was proposed with ladder factor. The calculation formula for transition probability was given in the model based on floor field, position vacancy degree and group attraction, and the evacuation strategy was presented. Meanwhile, the experiment studied the relationships of evacuation time, mean system velocity as well as pedestrian density. The result showed that the evacuation time could be reduced effectively when the mean system velocity and position vacancy had proper degree, and the bigger group had negative effect with the evacuation time, so the bigger group should be avoided in actual evacuation process.     

The excluded-volume effect in microscopic pedestrian simulations

We propose a pedestrian position update rule, which is added to a microscopic pedestrian model to avoid pedestrian overlap. In the rule, the step size of a pedestrian moving in a selected direction at each update is in inverse proportion to the repulsive actions imposed by other pedestrians moving in a direction with an exponential rate. The positions of the pedestrians are then updated in each small time interval. In this way, a barrier between the pedestrians can be generated, and after updating their positions the pedestrians do not overlap with each other. The modified model is compared to the original model through a simulation of the evacuation process of pedestrians in a closed area. The simulation results indicate that the modified model is superior to the original model in several aspects.     

通过博弈的室内行人疏散动力学研究

在室内行人疏散过程中,行人博弈对疏散效率有着重要的影响.本文把抵制博弈策略更新的强度定义为抵制强度. 为了研究抵制强度对疏散效率的影响, 通过在行人博弈策略更新的概率中引入抵制强度,基于元胞自动机模型数值计算在不同的行人密度, 出口宽度下疏散总时间随抵制强度变化的关系.结果表明: 室内行人疏散过程中, 抵制强度小会使得争抢行为极其容易蔓延. 当行人密度小且出口宽大时, 输入以急速疏散为主的规范信息,鼓励行人模仿优胜者更新博弈策略, 当行人密度大且出口狭小时, 输入以避让为主的规范信息抑制行人争抢,都能提高疏散效率. 最后找出不同条件下与最短疏散总时间相对应的优化抵制强度, 为提高室内行人疏散效率提供一个新的视角.     

Extraction and quantitative analysis of microscopic evacuation characteristics based on digital image processing

In this study, experiments of single-file pedestrian movement were conducted and the movement parameters of pedestrians were extracted with a digital image processing method based on a mean-shift algorithm. The microscopic characteristics of pedestrian dynamics, including velocity, density, and lateral oscillation, as well as their interrelations, were obtained and analyzed. Firstly, we studied the lateral oscillation phenomena of pedestrian movement. The result indicates that the trajectory of pedestrians presents a wavy form and the amplitude of the oscillation remains about 5.5 cm when the pedestrians move with free walking velocity, which is the velocity when there is no obvious interaction between sequential pedestrians; but when the movement velocity decreases to 0.27 m/s, the amplitude of oscillation increases to 13 cm. With increasing density, the velocity decreases and the amplitude of oscillation presents a linear increase trend. The increasing oscillation amplitude widens the occupation area of a pedestrian with low velocity, so as to make the moving efficiency even worse. Secondly, we studied the frequency of the oscillation; the result indicates that the frequency remains at 2 Hz when pedestrians move with a free walking velocity, but it presents a similar linear decrease trend when the velocity changes to a lower value. The decrease of oscillation frequency is also a negative feedback to the moving efficiency. Thirdly, it is found that with the increase of crowd density, the time interval between two sequential pedestrians increases, though the space gap between them decreases. The quantitative relation between time interval and crowd density is obtained. The study in this paper provides fundamental data and a basic method for understanding pedestrian dynamics, developing and validating evacuation models. The results are also expected to be useful for evacuation design.     

Simulation of pedestrian counter flow through bottlenecks by using an agent-based model

Considerable research has been conducted on the topic of unidirectional evacuations from exits. However, few studies aim at simulating counter flow through a bottleneck with complex conflict. This paper proposes an agent-based model to investigate bidirectional flow evacuation. Pedestrian speed is determined by the speed of the leading agent and the surrounding agents. The moving direction of pedestrian originates from four forces, namely, gradient force, repulsive force, resistance force, and random force. These four forces dominate the main stream of the pedestrian moving trajectory, the interaction between pedestrians and their local environment, the resistance or disinclination to movement, and the random variations and chaotic nature of pedestrian dynamics. The novelty of this research is in the agent-based model that combines the agent and forces while providing insights for the simulation of the pedestrian dynamic on the cognitive level. The experiment results show that the behavior that arises from this model is consistent with the observations from Guangzhou Metro and that this model could help capture the essence of pedestrian behavior near egresses.     

三维空间行人疏散的元胞自动机模型

为了有效刻画行人在三维空间中的疏散状况,结合阶梯因素提出了一种新的三维元胞自动机模型,该模型首先基于位置吸引力和碰撞可能性给出了行人移动概率的计算公式,并通过定义元胞演化过程阐述其疏散策略,同时,利用建立的仿真平台进行实验,深入分析了疏散时间、出口流率、出口宽度、初始行人密度以及系统平均速度之间的关系,以此获得更加符合实际情况的行人流特征,结果表明,疏散时间、出口流率与初始行人密度呈现正相关,而与出口宽度呈现负相关,并且系统平均速度和出口宽度对于最优疏散时间存在一个理想阈值。     

Modeling of pedestrian evacuation based on the particle swarm optimization algorithm

By applying the evolutionary algorithm of Particle Swarm Optimization (PSO), we have developed a new pedestrian evacuation model. In the new model, we first introduce the local pedestrian’s density concept which is defined as the number of pedestrians distributed in a certain area divided by the area. Both the maximum velocity and the size of a particle (pedestrian) are supposed to be functions of the local density. An attempt to account for the impact consequence between pedestrians is also made by introducing a threshold of injury into the model. The updating rule of the model possesses heterogeneous spatial and temporal characteristics. Numerical examples demonstrate that the model is capable of simulating the typical features of evacuation captured by CA (Cellular Automata) based models. As contrast to CA-based simulations, in which the velocity (via step size) of a pedestrian in each time step is a constant value and limited in several directions, the new model is more flexible in describing pedestrians’ velocities since they are not limited in discrete values and directions according to the new updating rule.     

双出口房间内疏散行人流的仿真和实验研究

为研究行人疏散过程中的路径选择行为, 提出了一个基于元胞自动机的行人微观模型, 并组织了三组双出口教室内的学生疏散实验. 模型中, 行人路径选择行为受其到出口距离、前方路径通行能力和行人间排斥力影响. 通过观察实验结果, 得到一些相关现象. 利用实验结果对模型参数进行校正. 利用校正模型对该教室内疏散学生流进行仿真, 结果表明 模型能有效地刻画教室内学生流的疏散特征, 疏散时间随学生人数线性增加. 该研究有助于类似场景中行人疏散策略和方案的制定. 关键词： 元胞自动机 行人疏散 仿真 实验     

Pedestrians' behavior in emergency evacuation:Modeling and simulation

The social force model has been widely used to simulate pedestrian evacuation by analyzing attractive,repulsive,driving,and fluctuating forces among pedestrians.Many researchers have improved its limitations in simulating behaviors of large-scale population.This study modifies the well-accepted social force model by considering the impacts of interaction among companions and further develops a comprehensive model by combining that with a multi-exit utility function.Then numerical simulations of evacuations based on the comprehensive model are implemented in the waiting hall of the Wulin Square Subway Station in Hangzhou,China.The results provide safety thresholds of pedestrian density and panic levels in different operation situations.In spite of the operation situation and the panic level,a larger friend-group size results in lower evacuation efficiency.Our study makes important contributions to building a comprehensive multi-exit social force model and to applying it to actual scenarios,which produces data to facilitate decision making in contingency plans and emergency treatment.     

基于元胞自动机的行人视线受影响的疏散流仿真研究

基于元胞自动机对视线受影响的行人疏散流进行仿真研究.模型根据行人视野半径将疏散空间划分为可见安全出口区域、可见墙壁区域和盲目区域;利用两个动态参数描述行人在不同移动区域内的疏散特征,从而决定行人的行为选择,包括行人定向移动、沿墙移动和正常疏散移动等行为.仿真研究了行人在墙壁上存在疏散指示标志的疏散空间内,视线受影响时采用随机定向寻墙沿墙移动疏散策略的情况下,行人视野半径对行人疏散时间的影响.研究表明,行人疏散时间不仅受行人视野半径的影响,而且还与安全出口的宽度和安全出口利用率有关.     

Simulation study on cooperation behaviors and crowd dynamics in pedestrian evacuation

Pedestrian evacuation is actually a process of behavioral evolution. Interaction behaviors between pedestrians affect not only the evolution of their cooperation strategy, but also their evacuation paths-scheduling and dynamics features. The existence of interaction behaviors and cooperation evolution is therefore critical for pedestrian evacuation. To address this issue, an extended cellular automaton(CA) evacuation model considering the effects of interaction behaviors and cooperation evolution is proposed here. The influence mechanism of the environment factor and interaction behaviors between neighbors on the decision-making of one pedestrian to path scheduling is focused. Average payoffs interacting with neighbors are used to represent the competitive ability of one pedestrian, aiming to solve the conflicts when more than one pedestrian competes for the same position based on a new method. Influences of interaction behaviors, the panic degree and the conflict cost on the evacuation dynamics and cooperation evolution of pedestrians are discussed. Simulation results of the room evacuation show that the interaction behaviors between pedestrians to a certain extent are beneficial to the evacuation efficiency and the formation of cooperation behaviors as well. The increase of conflict cost prolongs the evacuation time. Panic emotions of pedestrians are bad for cooperation behaviors of the crowd and have complex effects on evacuation time. A new self-organization effect is also presented.     

Modeling of pedestrian evacuation under fire emergency based on an extended heterogeneous lattice gas model

An extended heterogeneous lattice gas (E-HLG) model is developed by introducing an altitude factor into the heterogeneous lattice gas (HLG) model. The altitude factor is used to describe the position height of lattice sites. Evacuation features from a terrace classroom are investigated through simulations using both the model and experiments. To study evacuation processes under fire emergency, an agent-based fire and pedestrian interaction (FPI) model is proposed. It is supposed that the possible moving directions of a pedestrian depend on the environmental temperature field, which is simulated by the software FDS. The walking speed reduction due to the visibility worsening in the FPI model is described by a multi-grid method. It is found that simulation results based on the extended HLG model are in good agreement with the experiments. The altitude factor plays a guidance role to the evacuation, and the fire notably delays the evacuation due to both the harmfulness of the high temperature field and the change of evacuation routes which results in frequent local jamming and clogging.     

Study on evacuation behaviors at a T-shaped intersection by a force-driving cellular automata model

A force-driving cellular automata model considering the social force on cell movement, such as the desirous willing of a pedestrian to exit, the repulsive interaction among pedestrians or between pedestrians and obstacles, was set up to investigate the evacuation behaviors of pedestrians at a T-shaped intersection. And an analogical formulation, taking reference of the magnetic force, was introduced to describe the above repulsive actions. Based on the model, the evacuation behaviors of pedestrians were simulated in terms of different pedestrian density, distribution and corridor width, and then evacuation time was obtained and analyzed. Furthermore, an experiment was conducted to verify the results of the presented model. The results demonstrate that when the density of pedestrians is greater than a certain threshold, pedestrians of a certain direction would be jammed by the repulsion from pedestrians of the counter flow from another direction, and the evacuation time of the former would be longer, even though they are closer to the exit, which would possibly result in a serious casualty in an emergency circumstance. And the phenomenon has been validated by the experiments well. In addition, a corresponding critical corridor width related to different DOPs, beyond which the evacuation time could be decreased rapidly due to a strong degradation of jamming behaviors near the T-shaped intersection, was also discovered and predicted by the proposed model.     

Effect of a static pedestrian as an exit obstacle on evacuation

Building exit as a bottleneck structure is the last and the most congested stage in building evacuation. It is well known that obstacles at the exit affect the evacuation process, but few researchers pay attention to the effect of stationary pedestrians (the elderly with slow speed, the injured, and the static evacuation guide) as obstacles at the exit on the evacuation process. This paper explores the influence of the presence of a stationary pedestrian as an obstacle at the exit on the evacuation from experiments and simulations. We use a software, Pathfinder, based on the agent-based model to study the effect of ratios of exit width ($D$) to distance ($d$) between the static pedestrian and the exit, the asymmetric structure by shifting the static pedestrian upward, and types of obstacles on evacuation. Results show that the evacuation time of scenes with a static pedestrian is longer than that of scenes with an obstacle due to the unexpected hindering effect of the static pedestrian. Different ratios of $D/d$ have different effects on evacuation efficiency. Among the five $D/d$ ratios in this paper, the evacuation efficiency is the largest when $d$ is equal to $0.75D$, and the existence of the static pedestrian has a positive impact on evacuation in this condition. The influence of the asymmetric structure of the static pedestrian on evacuation efficiency is affected by $D/d$. This study can provide a theoretical basis for crowd management and evacuation plan near the exit of complex buildings and facilities.     

Simulation of pedestrian evacuation based on an improved dynamic parameter model

An improved dynamic parameter model is presented based on cellular automata. The dynamic parameters, including direction parameter, empty parameter, and cognition parameter, are formulated to simplify tactically the process of making decisions for pedestrians. The improved model reflects the judgement of pedestrians on surrounding conditions and the action of choosing or decision. According to the two-dimensional cellular automaton Moore neighborhood we establish the pedestrian moving rule, and carry out corresponding simulations of pedestrian evacuation. The improved model considers the impact of pedestrian density near exits on the evacuation process. Simulated and experimental results demonstrate that the improvement makes sense due to the fact that except for the spatial distance to exits, people also choose an exit according to the pedestrian density around exits. The impact factors α, β, and γ are introduced to describe transition payoff, and their optimal values are determined through simulation. Moreover, the effects of pedestrian distribution, pedestrian density, and the width of exits on the evacuation time are discussed. The optimal exit layout, i.e., the optimal position and width, is offered. The comparison between the simulated results obtained with the improved model and that from a previous model and experiments indicates that the improved model can reproduce experimental results well. Thus, it has great significance for further study, and important instructional meaning for pedestrian evacuation so as to reduce the number of casualties.     

Experimental study and numerical simulation of evacuation from a dormitory

The evacuation process of students from a dormitory is investigated by both experiment and modeling. We investigate the video record of pedestrian movement in a dormitory, and find some typical characteristics of evacuation, including continuous pedestrian flow, mass behavior and so on. Based on the experimental observation, we found that simulation results considering pre-movement time are closer to the experimental results. With the model considering pre-movement time, we simulate the evacuation process and compare the simulation results with the experimental results, and find that they agree with each other closely. The crowd massing phenomenon is conducted in this paper. It is found that different crowd massing phenomena will emerge due to different desired velocities. The crowd massing phenomenon could be more serious with the increase of the desired velocity. In this study, we also found the faster-is-slower effect. When the positive effect produced by increasing the desired velocity is not sufficient for making up for its negative effect, the phenomenon of the greater the desired velocity the longer the time required for evacuation will emerge. From the video record, it can be observed that the mass behavior is obvious during the evacuation process. And the mass phenomenon could also be found in simulation. The results obtained from our study are also suitable to all these buildings in which both living and resting areas occupy the majority space, such as dormitories, residential buildings, hotels (restaurants) and so on.     

Exit selection strategy in pedestrian evacuation simulation with multi-exits

A mixed strategy of the exit selection in a pedestrian evacuation simulation with multi-exits is constructed by fusing the distance-based and time-based strategies through a cognitive coefficient, in order to reduce the evacuation imbalance caused by the asymmetry of exits or pedestrian layout, to find a critical density to distinguish whether the strategy of exit selection takes effect or not, and to analyze the exit selection results with different cognitive coefficients. The strategy of exit selection is embedded in the computation of the shortest estimated distance in a dynamic parameter model, in which the concept of a jam area layer and the procedure of step-by-step expending are introduced. Simulation results indicate the characteristics of evacuation time gradually varying against cognitive coefficient and the effectiveness of reducing evacuation imbalance caused by the asymmetry of pedestrian or exit layout. It is found that there is a critical density to distinguish whether a pedestrian jam occurs in the evacuation and whether an exit selection strategy is in effect. It is also shown that the strategy of exit selection has no effect on the evacuation process in the no-effect phase with a low density, and that evacuation time and exit selection are dependent on the cognitive coefficient and pedestrian initial density in the in-effect phase with a high density.     

初始位置布局不平衡的疏散行人流仿真研究

行人初始位置布局不平衡的多安全出口疏散过程, 是行人疏散流仿真研究的热点. 利用行人流动态参数仿真模型, 在实际距离和假想距离"极大极小"路径选择机理的基础上, 改进假想距离的计算方法及其拥堵计算区域, 实现疏散过程的动态平衡; 提出行人位置布局的不平衡系数, 以描述疏散空间内行人初始位置布局的不平衡性. 从行人初始位置随机和固定布局的角度, 仿真研究正常疏散环境下行人布局的不平衡性对疏散时间的影响, 并将仿真结果与原始模型做对比分析. 研究表明, 模型能有效地实现行人流疏散过程的动态平衡, 行人疏散时间受行人位置或安全出口布局的影响较小, 而与安全出口总宽度、 行人的初始数量以及拥堵感知系数有关.     

Simulation of pedestrian evacuation strategies under limited visibility

Evacuation process under limited visibility is different from that under good visibility. To investigate the evacuation efficiency under limited visibility, different evacuation strategies including walking along the wall (S1), following the average movement direction (S2) and following the average position (S3) are proposed in this paper. Performances of these strategies under different visibilities, densities and exit widths are compared based on a revised social force model. Simulation results show that strategy S1 is more effective at low densities while strategy S2 and S3 are more efficient at high densities. It is noted that strategy S2 outperforms S3 under the same condition. In addition, strategy S1 is not sensitive to the change of exit width due to the movement mode of walking along the wall, while the following strategies (S2 and S3) have a better performance under the wide exit condition. The evacuation time for different proportions of pedestrians adopting one strategy in the mixed strategy situation is investigated and the optimal mixture proportion is also discussed. This study provides a new insight into the effect of different evacuation strategies on pedestrian evacuation, which is helpful for evacuees or organizers of public events to make an efficient evacuation plan under limited visibility.     

步行通道内行人流拉链现象的生成机理与仿真研究

以步行通道内的单向行人流为研究对象,分析研究行人拉链现象的生成机理,并建立基于Voronoi图的速度修正模型对其仿真研究.首先,从行人追求视野最佳和步行舒适的角度分析拉链现象的生成机理,以行人的视野关注和视野遮挡描述影响行人移动过程中产生拉链偏移的因素;以行人局部密度描述行人的步行舒适度;引入拉链敏感系数描述行人客观偏移的意愿程度;提出单个行人侧向偏移的机制,获得行人最佳的偏移位置.然后,构建基于Voronoi图的行人速度修正仿真模型,考虑行人是否有偏移倾向的主观意愿,并嵌入偏移规则,模拟再现行人的拉链现象.仿真发现:行人的拉链层数与通道宽度成正比,该模型速度密度关系图与实证数据吻合较好;与不考虑拉链效应相比,倾向主动进行侧向偏移的行人占比越大,越有助于提高通道内行人的移动速度、舒适度和空间利用率.