1.Key Laboratory of Transport Industry of Big Data Application Technologies for Comprehensive Transport, Ministry of Transport, Beijing Jiaotong University, Beijing 100044, China 2.College of Civil Engineering and Architecture, Henan University of Technology, Zhengzhou 450001, China
Fund Project:Project supported by the National Natural Science Foundation of China (Grant Nos. 71771013, 71621001), the National Key R&D Program of China (Grant No. 2019YFF0301403), the Special Funds for Fundamental Scientific Research Operation Fees of Central Universities, China (Grant No. 2019JBM041), and the Singapore Ministry of Education (MOE) AcRF Tier 2 (Grant No. MOE2016-T2-1-044)
Received Date:30 September 2020
Accepted Date:23 October 2020
Available Online:09 March 2021
Published Online:20 March 2021
Abstract:In this study, the unidirectional pedestrian flow in the corridor is taken as a research object, the generation mechanism of the pedestrian zipper phenomenon is analyzed, and a velocity correction model based on the Voronoi diagram is established for the simulation research. First, the generation mechanism of the pedestrian zipper phenomenon is analyzed from the perspective of optimal visual field and walking comfort of pedestrians. Then the visual attention and visual occlusion of pedestrians are used to describe the factors which affect the zipper deviation during pedestrian movement, the local density of pedestrians is used to describe the walking comfort of pedestrians, the zipper sensitivity coefficient is adopted to describe the willingness of pedestrians to move objectively, and the mechanism of lateral deviation of a single pedestrian is considered to obtain the optimal deviation position of pedestrians. Besides, the Voronoi diagram is introduced to effectively determine the pedestrians surrounding the target pedestrian within the visual field. And the influence of surrounding pedestrians with different distances and directions on the moving velocity of the target pedestrian based on the Voronoi diagram is considered. Then, a velocity correction model of pedestrians based on the Voronoi diagram is constructed, whether the pedestrian has a subjective willingness to deviate is considered, and the deviation rule is embedded to simulate and reproduce the zipper phenomenon of pedestrians. The simulation results truly reproduce the normal pedestrian flow through the corridor and show that our model can overcome the deficiency of the jitter and overlap phenomenon of the traditional social force model. The self-organized pedestrian flow with uniform distribution and the pedestrian zipper effect can also be observed. Furthermore, through the simulation results, we can see that the number of zipper layers for pedestrians is proportional to the width of the corridor. The comparison of simulated pedestrian data with the empirical data indicates that the fundamental diagram of velocity-density relation of our model is in good agreement with the empirical data. A comparison between with and without considering the zipper effect shows that the larger the proportion of pedestrians actively willing to laterally deviate, the more helpful it will be to improve the moving velocity, comfort and space utilization of pedestrians in the corridor. Keywords:pedestrian dynamics/ pedestrian simulation/ zipper effect/ Voronoi diagram
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2.1.拉链现象
行人流自组织现象是指行人流内部个体行人之间在无外界力量指导下, 出于自身因素和作用, 自发组织和形成的行人流宏观现象. 自组织现象之一的拉链效应[30]是指通道内多条单向行人流队列之间的相互重叠现象. 在通道内运动的单向行人流, 把每一列行人看作一层, 会自发产生层或小道, 不同层间的行人相互交错, 各层行人均占用相邻层的空间, 形成“拉链”现象, 如图1所示. 该现象的产生主要是由于行人需要尽可能地利用通道中的可行空间, 在确保自身行走空间的同时提高自己的视野. 图 1 瓶颈中的行人拉链现象[30] Figure1. Zipper phenomena of pedestrians in a bottleneck[30].
行人在移动过程中, 手脚有节奏的依次来回摆动, 其所占动态空间投影区域类似圆形. 在相同方向行走过程中, 两相邻行人组成的行人间基本位置形式可分为并排、斜列、直列3种, 如图3所示. 图 3 两相邻行人同方向行走形态 (a)行人行走形态; (b)两行人行走并排形式; (c)两行人行走斜列形式; (d)两行人行走直列形式 Figure3. Walking pattern of two adjacent pedestrians in the same direction: (a) The real single pedestrian walking pattern; (b) two adjacent pedestrians walking side by side; (c) two adjacent pedestrians walking in a diagonal pattern; (d) two adjacent pedestrians walking in a straight line.
通过分析行人实验[33], 研究通道宽度与行人拉链现象之间的关系, 可以发现当通道宽度仅能容纳一个行人通过时, 行人以直列形式排列, 如图4(a)所示; 当通道宽度不足以容纳两个行人并排通过时, 行人以直列、斜列形式排列, 如图4(b)所示; 当通道宽度足以容纳多个行人并排通过时, 行人之间的并排、斜列、直列多种排列形式均会出现, 如图4(c)所示. 图4(b)和图4(c)是典型拉链现象的表现形式. 图 4 行人拉链现象表现形式 (a)单列行人截图[33]与行人直列形式对比; (b)两列行人截图[33]与行人直列、斜列形式对比; (c)多列行人截图[33]与行人多种排列形式对比 Figure4. Manifestation of pedestrian zipper phenomenon: (a) The comparison of single-column pedestrian screenshot[33] with pedestrians in-line pattern; (b) the comparison of two-column pedestrian screenshot[33] with pedestrians in-line and diagonal patterns; (c) the comparison of multi-column pedestrian screenshot[33] with multiple arrangement patterns of pedestrians.
22.3.视野最佳 -->
2.3.视野最佳
行人行走时一般目视前方, 在视野后方的行人基本不会对前方行人的行为决策产生影响. 在行人有效视野范围内, 也不是所有角度和距离都会对行人产生同样的影响. 显然正前方是行人最为关注的视野区域, 对行人的行为决策影响最大; 而从中间向两侧的视野区域对行人行为决策的影响程度迅速衰减. 以图5为例, 移动行人${P_1}$的视野被行人${P_2}$, ${P_3}$, ${P_4}$阻挡, 行人${P_1}$的可见视野区域是${Z_2}$, ${Z_4}$, ${Z_6}$, 不可见视野区域是${Z_1}$, ${Z_3}$, ${Z_5}$. 显然${Z_3}$区域阻挡了行人${P_1}$正前方的主要观察视野和道路, 对行人${P_1}$行为决策的影响最大, 是促使行人${P_1}$侧向偏离的主要诱因; ${Z_5}$区域虽然对行人${P_1}$观察周围视野产生一定遮挡, 但不在行人${P_1}$前进道路上, 对行人${P_1}$行为决策的影响较弱; ${Z_1}$区域处于行人${P_1}$观察视野的边缘区域, 对行人${P_1}$行为决策的影响最弱, 几乎不会引起行人${P_1}$的特别关注. 图 5 有效视野区域内的行人视野关注和遮挡(橙色遮挡区域是目标行人最为关注和对目标行人影响最大的区域, 蓝色遮挡区域对目标行人的影响较弱) Figure5. Pedestrian vision attention and occlusion in the effective vision area (the orange shaded area is the area that the target pedestrian pay the most attention to and has the greatest influence on the target pedestrian, while the blue shaded area has a relatively weak influence on the target pedestrian).
考虑视野对行人行为决策的影响, 以行人视野关注和视野遮挡描述影响行人侧向偏离的因素. 视野关注表示行人对不同视野区域的关注程度. 同时, 不同视野区域对行人行为决策的影响程度也不同. 视野遮挡表示在行人有效视野区域内, 被遮挡视野区域面积占行人有效视野区域面积的比重. 正前方区域是行人视野最为关注和对行人视野遮挡影响最大的区域. 此外, 即使是同一视野方向, 不同距离行人对目标行人视野的遮挡影响程度也不同. 距离越近, 对目标行人视野遮挡越大; 距离越远, 对目标行人视野遮挡度越小. 以图6为例, 行人${P_3}$和${P_5}$相对目标行人${P_1}$在同一视野方向, 与行人${P_1}$的距离分别是${l_{13}}$和${l_{15}}$, 对行人${P_1}$视野的遮挡角度分别是${\sigma _{13}}$和${\sigma _{15}}$, 遮挡范围分别是${Z_5}$和$Z_5'$. 显然${l_{15}} > {l_{13}}$, ${\sigma _{15}} < {\sigma _{13}}$, 但$Z_5' < {Z_5}$. 图 6 不同距离行人对目标行人视野的遮挡程度 Figure6. Occlusion degree of the target pedestrian’s vision by surrounding pedestrians at different distances
22.4.步行舒适 -->
2.4.步行舒适
当通道宽度足以容纳多个行人通过时, 在观察行人拉链现象过程中, 可以引入行人局部密度, 描述行人的步行舒适度. 在Voronoi图中, 假设行人${P_i}$所对应Voronoi元胞的面积是${a_i}$, 则其局部密度为${\rho _i} = 1/{a_i}$[27]. 当行人局部密度较低时, 行人拥有较大的个人空间和较好的步行舒适度, 行人之间会出现并排、斜列、直列等形式, 且行人的步行速度不受影响, 行人以自由流速度移动, 如图7(a)所示; 当行人局部密度较高时, 行人的个人空间较小, 行人需要充分利用步行设施空间移动, 行人的步行舒适度会受到影响, 且会影响和限制后面行人的步行速度, 行人之间会出现各种排列形式, 如图7(b)所示. 图 7 不同行人局部密度下的拉链现象示意(绿色、黄色、橙色分别表示行人局部密度由低到高) (a)行人局部密度较低时; (b)行人局部密度较高时 Figure7. The zipper phenomenon of pedestrians under different local density (green, yellow and orange respectively represent the local pedestrian density from low to high):(a) When the local pedestrian density is relatively low; (b) when the local pedestrian density is relatively high.
同时, 行人是否会进行侧向偏移还与自身的主客观偏离意愿和习惯有关. 以图8为例, 当通道宽度正好可以允许两个行人并排通过时, 若行人的偏离意愿程度较低, 行人之间有可能形成规则形状的直列, 如图8(a)所示; 当通道宽度不足以允许两个行人并排通过时, 若行人的偏离意愿程度较高, 行人之间会自发形成不规则形状的拉链, 如图8(b)所示; 当通道宽度可以允许多个行人并排通过时, 若行人的偏离意愿程度较高, 行人在潜意识驱动下会自发进行侧向偏离, 追求更宽广的可见视野和步行舒适度, 形成典型的拉链现象, 如图8(c)所示. 图 8 不同偏离意愿下的拉链现象示意 (a)窄通道行人偏离意愿较低时; (b)窄通道行人偏离意愿较高时; (c) 宽通道行人偏离意愿较高时 Figure8. Zipper phenomenon of pedestrians under different deviation intentions: (a) When the deviation intention of pedestrians in narrow corridors is relatively low; (b) when the deviation intention of pedestrians in narrow corridors is relatively high; (c) when the deviation intention of pedestrians in wide corridors is relatively high.
图 10 行人拉链效应的最佳形态 Figure10. The best form of pedestrian zipper effect.
22.5.偏移机制 -->
2.5.偏移机制
通过观察, 分析行人追求视野最佳和步行舒适形成拉链现象的行为机制. 假设不考虑行人个体和主观偏移意愿的差异, 认为行人均有主观偏移意愿. 当通道宽度足够容纳多个行人并肩通过且行人整体密度较大时, 行人会呈现各种排列形式. 其中, 斜列形式在一定程度上是行人侧向偏移的结果, 是行人拉链现象的主要表现形式. 在行人行走过程中, 若前方行人阻挡了后方行人的视野和道路, 会影响和限制后方行人行走的舒适度和步行速度. 此时, 为了追求更好的可见视野和行走舒适度, 后方行人会进行侧向偏移, 形成斜列形式. 以3个毗邻行人作为基本研究单元, 当行人处于图10所示的视野最佳和步行舒适的拉链稳定状态时, 在有效可见距离L内, 在目标行人正前方视野遮挡下, 行人可获得的最佳可见关注视野为${\theta _{\rm{s}}}$, 如图11所示. 设定行人半径为${r_{\rm{h}}}$, 头部半径为${r_{\rm{s}}}$, 目标行人相对正前方视线的最佳单侧可见视野范围标准值为${\theta _{\rm{h}}}$, 具体表达式为 图 11 行人基本单元的拉链稳定状态(阴影区域为目标行人正前方视野遮挡区域, 非阴影区域为目标行人有效可见视野区域) Figure11. Zipper stability state of pedestrian basic unit (the shadow area is the vision occlusion area and the non-shaded area is the effective visible area in front of the target pedestrian).
以行人#4为例, 可以看到在不同仿真时间步, 行人#4进行了明显的拉链效应偏移, 以获得更好的视野和步行舒适度, 如图19所示. 图 19 行人#4在不同仿真时间步的拉链效应偏移截图 Figure19. Screenshot of zipper effect of pedestrian #4 at different simulation time steps.
24.2.对比分析 -->
4.2.对比分析
在直通道中随机产生20个行人, 随着通道宽度$B$的增加, 行人自主选择的空间逐渐变大, 行人可以充分地进行拉链效应偏移. 当行人形成稳定的行人流时, 可以观察到不同宽度通道中形成不同的行人队列层数, 通道宽度越大, 行人队列层数越多, 与行人实验[33]的结论相吻合, 如图20所示. 图 20 行人拉链层数与通道宽度关系 Figure20. Relationship between the number of pedestrian zipper layers and the width of the corridor.
为了获得行人速度与密度的关系, 对不同密度条件下(人/m2)的行人进行单向循环流仿真, 并通过基本图验证模型的可靠性. 在每个行人密度点的仿真实验中, 最开始行人随机地分布于走廊中, 行人的目标点位于走廊上端, 每次仿真实验重复10次, 每次持续90个仿真时间步, 实验的前30个仿真时间步当做热身时间, 后60个仿真时间步的数据用于统计分析. 图21将速度修正模型与其他实证研究的数据进行了对比, 可以发现速度修正模型的速度-密度关系与实证数据符合得较好[37-41]. 图 21 直通道单向行人流基本图[37-41](该模型仿真数据与实证数据(Older[37], Mori[38], Zhang[39], Weidmann[40], Hankin[41])进行对比) Figure21. Fundamental diagram of unidirectional pedestrian flow in the corridor[37-41]. Actual data (Older[37], Mori[38], Zhang[39], Weidmann[40], Hankin[41]) are gathered to compare with our model.
通过改变行人拉链效应主观偏移意愿与无偏移意愿的占比$u$, 可以得到不同密度下, 行人主观偏移意愿占比与行人平均速度的关系, 如图22所示; 也可以获得不同密度下, 行人主观偏移意愿占比与行人平均局部密度的关系, 如图23所示. 可以发现, 与不考虑拉链效应相比, 倾向主动进行拉链效应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, 与行人实验[30]的研究结果相符合. 图 22 不同密度下行人主观偏移意愿占比与行人平均速度关系 Figure22. Relationship between the proportion of pedestrian subjective deviation intention and pedestrian average velocity under different overall densities.
图 23 不同密度下行人主观偏移意愿占比与行人平均局部密度关系 Figure23. Relationship between the proportion of pedestrian subjective deviation intention and pedestrian average local density under different overall densities.