What affects pedestrian crossing difficulty at urban intersections in a developing country?

In developing countries, road traffic crashes involving pedestrians have become a foremost concern. At present, road safety assessment plans and selection of interventions are primarily restricted to traditional approaches that depend on the investigations of historical crash data. However, in developing countries such as India, the availability, consistency, and accuracy of crash data are major concerns. In contrast, proactive approaches such as studying road users' risk perception have emerged as a substitute method of examining potential risk factors. An individual's risk perception offers vital information on probable crash risk, which may be beneficial in detecting high-risk locations and major causes of crashes. Since the pedestrian fatality risk is not uniform across the urban road network level, it may be expected that pedestrians' perceived risk measured in terms of “crossing difficulty” would also vary across the sites. In this perspective, the present paper establishes a mathematical association between the pedestrians' perceived “crossing difficulty” and actual crashes. The model outcome confirms that pedestrians' perceived crossing difficulty is a good surrogate of fatal pedestrian crashes at the intersection level in Kolkata City, India. Subsequently, to examine the impact of traffic exposures, road infrastructure, land use, spatial factors, and pedestrian-level attributes on pedestrians' “crossing difficulty”; a set of Ordered Logit models are developed. The model outcomes show that high vehicle and pedestrian volume, vehicular speed, absence of designated bus stop, the presence of inaccessible pedestrian crosswalk, on-street parking, lack of signalized control (for both vehicle and pedestrian), inadequate sight distance, land use pattern, slum population, pedestrian-vehicular post encroachment time, waiting time before crossing, road width, and absence of police enforcement at an intersection significantly and positively increase pedestrian's crossing difficulty at urban intersections. To end, the model findings are advantageously utilized to develop a set of countermeasures across 3E's of road safety.     

Exploring pedestrian surrogate safety measures by road geometry at midblock crosswalks: A perspective under mixed traffic conditions

Pedestrian safety is generally assessed using frequency of crashes, based on historical data, for a given transportation facility. However, the lack of good and reliable crash data has hampered its apposite analyses and in evaluating the effectiveness of pedestrian safety programs. To overcome this gap, traffic conflict technique (TCT) which relies mainly on the observations of critical traffic situations for safety analysis were developed. However, the applicability of TCTs and related measures under varying non-lane based heterogeneous traffic conditions prevailing in countries such as India is not widely explored. This paper attempts to evaluate pedestrian safety at urban midblock crosswalk using different surrogate safety measures, including vehicle crossing speed, post encroachment time (PET), yielding compliance of driver as well as pedestrian, and conflict rate. The number of conflicts were observed to increase as the average vehicle crossing speed increases, indicating that pedestrians are extremely vulnerable while crossing the road. The PET value for the smaller vehicles, such as two-wheelers and three-wheelers, is recorded to be lower than the heavy vehicles, such as trucks and buses. With the addition of one lane, there is a significant decrease in the PET value. The average PET values for the vehicle on eight-lane divided road is less than the six-lane divided, four-lane divided, and two-lane undivided roads. Further, the yielding compliance of the driver as well as of the pedestrian depends on the crossing speed of the approaching vehicle and the type of road geometry. Further, the rate and severity of conflicts increased with a decrease in the pedestrian crossing speed. The yielding behaviour of the drivers as well as the pedestrian's yielding compliance varies by location, highlighting the effect of individual and demographic characteristics on pedestrian crossing behaviour.     

城市行人过街速度研究

为研究城市平面行人过街的速度及差别,分别对哈尔滨市冬夏两季的信号交叉口、无信号交叉口、环形交叉口、路段人行横道和自由过街5种不同过街条件下的行人过街速度进行调查。分析了冬季与夏季和不同过街条件下行人过街速度的变化以及形成原因;分析了行人年龄、性别、人行横道长度、过街行人数量和绿灯时间对行人过街速度的影响;采用数理统计方法,用15%位速度作为行人过街的设计速度,提出冬夏两季不同过街条件下的行人过街设计速度推荐值。     

信号交叉口右转机动车与行人冲突运动模型

在一些信号交叉口,右转机动车的转弯行为不受信号控制,容易与过街行人发生冲突。现有冲突研究的内容多为冲突判别和冲突分级研究,对人车冲突运动过程研究相对较少。为减少交通冲突,提高行人过街安全性,提出一种新的右转机动车与行人冲突运动过程的仿真模型。研究右转车辆的决策过程,分析人车冲突机理。建立人车冲突模型,依据实际调查所获得的车辆速度和可接受间隙数据,对模型参数进行标定。对模型进行仿真分析,通过比较冲突时间、后侵占时间、安全减速度、间距时间4个冲突严重性指标,选择后侵占时间(PET)这一评价指标进行安全评价。仿真得到的车辆速度和 PET 数据与调查得到数据相比误差不超过5%,验证了模型的有效性。通过灵敏度分析,小交叉口 PET 提高了10%,说明小交叉口有助于降低冲突的严重性。      

Quality of pedestrian flow and crosswalk width at signalized intersections

Among various pedestrian facilities, signalized crosswalks are the most complex and critical ones. Their geometry and configuration including width, position and angle directly affect the safety, cycle length and resulting delays for all users. Existing manuals do not provide clear and rational specifications for the required crosswalk width under different pedestrian demand combinations and properties. Furthermore, they do not consider the bi-directional flow effects on crossing speed and time when addressing pedestrian flow at signalized crosswalks. However, quantifying the effects of such interactions on the behavior of pedestrian flow is a prerequisite for improving the geometric design and configuration of signalized crosswalks. The objective of this paper is to develop a methodology for estimating the required crosswalk width at different pedestrian demand combinations and a pre-defined LOS. The developed methodology is based on theoretical modeling for total pedestrian platoon crossing time, which consists of discharge and crossing times. The developed models are utilized to generate the fundamental diagrams of pedestrian flow at signalized crosswalks. A comprehensive discussion about the effects of bi-directional flow and various pedestrian age groups on the characteristics of pedestrian flow and the capacity of signalized crosswalks is presented. It is found that the maximum reduction in the capacity of signalized crosswalks occurs at roughly equal pedestrian flows from both sides of the crosswalk. By utilizing existing LOS thresholds for pedestrian flow at signalized crosswalks, the required crosswalk widths for various pedestrian demand combinations are proposed for implementation.     

无信号控制人行横道处行人过街特性探析

行人是交通环境中的"弱势群体",尤其是在无信号控制人行横道处,研究行人交通特性是提出改善行人安全措施的前提。本文初步对无信号控制人行横道处人车干扰运行和行人过街运动特性进行定性分析,并选取长春市南湖大路上具有代表性的无信号控制人行横道进行实地观察和试验,定量分析行人到达人行横道规律和行人过街速度特性,其中重点分析年龄、性别和人群中行人数量对行人过街速度的影响。按照年龄将行人分为中、青年人,老人,儿童;按照性别将行人分为男性行人和女性行人;人群中行人数量主要选取1,2,3及4人以上进行研究。这些数据和分析结论对下一步针对实地情况提出改善行人交通安全的方案提供了基本的理论依据。     

考虑礼让行人的信号交叉口配时优化方法

为提高机动车礼让行人背景下的人车通行效率,研究了基于叠加相位设计的信号交叉口配时优化方法.以西安市1个典型交叉口为例,分析机动车与过街行人冲突情况;在Webster配时模型的基础上,提出叠加相位设计与人车冲突时空分离策略相结合的信号配时优化方法,并给出行人信号早启时间、人车绿时分离设置阈值的计算方法;运用VISSIM仿...     

考虑动态车速的双周期干线信号协调控制多目标优化

干线协调控制通常以干线方向通行效率最大为目标，导致一些小型交叉口次路方向延误较大。针对该问题，基于车路协同环境，研究了车速引导下的双周期干线多目标优化方法。针对上游交叉口饱和交通流与非饱和交通流2种情况，提出了考虑排队消散和相位差的动态车速引导模型。以干线延误、通行能力、停车次数，双周期交叉口次路方向延误为优化目标，构建了车速引导下的双周期干线多目标优化模型，采用遗传算法对模型进行求解。基于COM接口，采用Python和Vissim搭建车路协同仿真环境，以北京市两广路的3个路口为例进行仿真验证。对比了本文模型与原配时方案、无车速引导下双周期干线多目标优化模型的效果，结果表明，本文模型相比于原配时方案和无车速引导下多目标优化模型，干线平均延误分别减少19.6%，8.3%，通行能力分别提升5.6%，8.4%，平均停车次数分别减少11.2%，24.2%，双周期交叉口次路方向平均延误分别减少33.9%，5.8%，表明本文模型将速度引导与多目标优化相结合，提高了双周期干线的通行效率，降低了双周期交叉口次路方向的延误，达到了干线和双周期交叉口共同优化的目的。      

Evaluation of a brake assistance system (BAS) using an injury severity prediction model for pedestrians

Through the years, traffic engineers and researchers have developed a variety of countermeasures to enhance pedestrian safety. Pedestrian-vehicle collisions are regarded as the most serious type of accident since they incur high fatality rates. A fundamental concept in developing effective countermeasures is to analyze pedestrian-vehicle collisions scientifically, which can identify the causes of accidents and accident severity. The objective of this study was to investigate the pedestrian safety benefit of the brake assistance system (BAS) and a functional requirement associated with BAS, namely the time needed to safely detect a pedestrian ahead. An injury severity prediction model for pedestrians was developed to systematically evaluate the BAS in this study. Ordered multinomial logistic regression analysis was used to establish a statistical model capable of predicting pedestrian injury severity. In addition to vehicle characteristics, collision speed and pedestrian characteristics were used as independent predictor variables. The outcomes of this study would be useful in directing the development of safety policies and technologies associated with pedestrian safety.     

信号交叉口行人安全岛设计

以北京等大城市信号交叉口行人过街安全问题为研究对象,对40个未设置行人安全岛和5个设置行人安全岛的信号交叉口进行了现场观测,研究分析了为方便行人二次过街、在道路中间分隔带设置行人安全岛的必要性,并提出了一种适合我国国情的安全岛设计型式。     

人行横道交通安全性改善措施研究

近几年来,我国各级政府对行人过街安全非常重视,很多地方开展了改善人行横道安全方面的创新,取得了一定的成效,但部分措施的科学性及实效性值得商榷。对此,首先梳理了人行横道相关法律法规、规范,也是目前人行横道设置的主要依据。进而,列举了部分人行横道的创新措施,包括:调整人行横道样式、智能斑马线的应用、推广礼让斑马线。最后,基于交通工程基本原理,分析改善人行横道安全应关注的几个方面,重点处理好人行横道控制方式、视距与视区、照明与反光三大因素,并提出改善安全性的5条具体措施,其中部分措施是对现行规范的创新,为人行横道的科学设置提供参考。     

Development of probabilistic pedestrian fatality model for characterizing pedestrian-vehicle collisions

Pedestrian-related accidents are considered to be the most serious of traffic accidents due to the associated high fatality rates. In Korea, pedestrian fatalities accounted for approximately 40% of all traffic-related fatalities in 2004. Significant efforts have been made to develop effective countermeasures for pedestrian-vehicle collisions. A basis for devising such countermeasures is to understand the characteristics of pedestrian-vehicle collisions. This study develops a pedestrian fatality model capable of predicting the probability of fatality in pedestrian-vehicle collisions. Binary logistic regression and a probabilistic neural network (PNN) are employed to estimate the probability of pedestrian fatality. Pedestrian age, vehicle type and collision speed are used as independent variables of the fatality model. The models developed herein are valuable tools that can be used to direct safety policies and technologies associated with pedestrian safety.     

路段感应式信号控制行人过街系统设计

为保障路段行人安全过街,提高行人过街效率,设计了基于感应控制的路段行人安全过街系统.该系统分别采用视频和感应线圈实现对过街行人和路段车辆的自动检测,并据此设计行人过街感应信号控制方案,辅以“减速带式”人行横道、路段行人过街通道灯和智能人行道护栏3种过街辅助设施,实现时空上的人车分离.     

典型信号控制交叉口行人专用相位设置阈值研究

针对目前城市道路交叉口中人车混行现象,综合考虑效率与安全两方面因素,选取延误成本和冲突成本分别作为效率与安全的评价指标,构建有(无)行人专用相位信号控制模式的交叉口运行成本模型.模型的延误成本中,行人和非机动车延误考虑了信号延误、冲突延误以及绕行延误;冲突成本则基于交通冲突理论,以车头时距判断机动车与行人和非机动车是否发生冲突为指标,并根据机动车及行人和非机动车达到分布确定冲突概率.最后,通过北京市四道口交叉口验证了该模型的适用性,并基于遗传算法求得典型信号控制交叉口中行人专用相位设置的阈值在750~900人/h浮动,随着车流量的增长,行人专用相位的设置对行人流量的要求呈现先降后升的趋势.为城市道路交叉口信号配时设计提供了理论支撑,保障行人及非机动车安全、舒适、方便、尊严的出行.      

基于车路协同环境的信号交叉口车速引导方法

针对现有的车速引导模型存在未综合考虑车辆跟驰行为、引导场景划分较粗略等问题，研究了4种基于车路协同环境下实时优化各车的车速引导模型。对车辆进行所属车辆列队划分，考虑车速引导影响对FVD跟驰模型进行改进。以车辆列队为引导单元，将车辆可能面临的交通状况细分为8种引导场景，以引导车辆不停车或少停车通过交叉口为目标，直接优化车辆加/减速度，建立车辆列队后车根据改进的跟驰模型计算目标跟驰加/减速度，并与头车组成列队以同一目标车速通过交叉口停车线的4种车速引导模型。以南昌市海棠北路/枫林西大街交叉口为例进行仿真验证，结果表明，所提出的车速引导模型能使车辆行程时间减少18.9%，最大排队长度减少58.8%，延误减少60.8%，燃油消耗减少36.4%，且适用于不同交通饱和状态，对提高信号交叉口通行效率和减少车辆燃油消耗有显著效果。      

道路交通岛安全防护设计的探讨

道路平交路口是城市交通网络中重要节点,是行人过街、车辆转换方向重要位置,也是交通事故频发的位置。道路路口的交通岛设立,原本就是为了保证行人的人身安全,但不合理设计的道路交通岛似乎成了“夺命岛”,让遵守交通规则的行人受到了生命安全威胁。本文通过路口交通岛现状分析、交通事故案例分析,对路口交通岛提出有效、可行的设计思路及设计理念,以提高交通岛的防护性及安全性。     

Hierarchical distributed coordination strategy of connected and automated vehicles at multiple intersections

In this paper, we present a hierarchical distributed coordination strategy for connected and automated vehicles (CAVs) that are travelling through multiple unsignalized intersections. The control strategy focuses on the improvement of vehicle fuel efficiency and system mobility. In presence of wireless communication among the involved CAVs and the intersection controllers, our coordination strategy focuses on leading the CAVs travel through a road network without conventional traffic light control and ensuring collision avoidance at the intersection areas. We propose a three-layered coordination strategy in this paper. First, we evaluate the road desired average velocity considering both upstream and downstream traffic to speed up the traffic density balance. Second, the intersection controllers optimally assign reference velocity to each vehicle based on the minimization of velocity deviation from its current velocity and collision avoidance at the intersections. Finally, fast model predictive control (F-MPC) is applied for each vehicle to track their reference velocity in a computationally efficient manner. Two simulation scenarios with different difficulty levels have been implemented on a two-interconnected intersection network. Simulation results indicate the feasibility and scalability of the proposed method, as well as vehicle fuel efficiency and system mobility improvement.     

信号交叉口基于出发时刻预测的生态驾驶方法

在城市道路交通中,信号交叉口区域内车辆频繁停车启动的现象,加剧了整体交通流的能源消耗、污染排放与车辆延误。为了减少信号交叉口启停波现象对整体交通流产生的负面影响,以面向未来人工驾驶车辆(HDV)/智能网联车辆(CAV)混合构成的新型混合交通环境为基础,提出了一种基于出发时刻预测的生态驾驶方法,通过优化CAV的驾驶轨迹,减少交叉口区域的车辆延误和能源消耗。首先,对混合交通流的基本图模型进行了分析,根据启停波影响范围,划分CAV通过交叉口的驾驶场景;然后,建立了子区渗透率对饱和车头时距的影响关系,预测了CAV以当前饱和车头时距通过交叉口的时间;最后,结合车辆与交叉口的距离,利用分段三角函数模型,生成其通过交叉口的速度限制曲线,并将优化速度嵌入到智能车辆的跟驰模型中作为限制速度,从而使CAV在无法通过当前绿灯窗口的条件下,实现提前减速,在通过交叉口区域后解除速度限制,切换回自身的跟驰模型。此外,还提出了平均综合效能这一指标来综合评价驾驶策略在效率和能耗2个方面的性能,并将提出的基于出发时刻预测的生态驾驶方法与传统网联车辆控制方法、经典交叉口节能控制方法进行了对比。研究结果表明:提出的出发时刻预测方法可以精确预测CAV在交叉口的出发时刻,有效减少车辆的能源消耗与污染排放,同时提高信号交叉口的通行效率;在渗透率大于60%情况下,该方法对系统效能的提高达到12%左右,在10%渗透率条件下也可以达到6%的效能增益;在交通饱和流率在0.5~0.9的范围内时,系统的效能增益较明显。     

交叉口人行横道通行能力研究

人行横道通行能力是确定行人过街设施的基础参数。通过分析信号交叉口处人行横道混合交通特征,提出了一定周期时长和单位人行横道宽度的人行横道绿灯时间内的实际通行能力计算公式;以可接受间隙理论为基础,利用概率论的方法,推导出了无信号交叉口处人行横道的通行能力计算公式,并通过实例验算,具有一定的实用价值。     

基于虚拟车队的自动交叉路口车辆时序优化模型

智能网联汽车可通过彼此交互协同安全地通过交叉路口,自动交叉路口控制已成为未来发展趋势。为解决现有基于预约的自动交叉路口控制模型未全局优化车辆通过顺序及模型非线性导致求解效率低等问题,提出一种基于虚拟车队的自动交叉路口车辆时序优化模型,实现车辆通过时序的高效全局优化。首先,为构建到达安全时间间隔约束,基于车辆冲突分析计算交叉口进口道停车线到各相互作用点的距离。其次,为便于建模和求解,基于时间维度构建虚拟车队并形成车辆索引序列。然后,以交叉口车辆总延误最小为优化目标,车辆通过控制区段的最小行程时间和到达冲突区域边界的安全间隔为约束条件,构建自动交叉路口车辆通过时序非线性优化模型。在此基础上,引入0-1变量将该模型转化为混合整数线性规划模型,并基于开源求解器CBC对模型进行求解。最后,设计数值仿真试验验证模型的有效性并进行了模型的参数敏感性分析。研究结果表明:所构建模型在不同交通需求下优化效果均优于基于"先到先服务"规则的模型,车均延误和最大单车延误能够减少61.50%和39.73%;当安全间距和优化周期较大时,构建模型的延误控制效果更为显著;模型和算法为未来智能网联环境下自动交叉路口控制提供了一种可选的方法。