城市主要道路平面交叉口安全管理方法

文章基于现今城市干道平面交叉口交通流量密集的状况,分析讨论影响平面交叉口安全管理的因素,提出了交叉口安全管理方法和一些改进措施,为提高城市道路交叉口的交通安全管理提供依据。     

市政道路平面交叉口的交通组织设计

市政道路平面交叉口处路况复杂且多变,为了更好地建设市政道路平面交叉口,做好交叉口的交通组织设计,对市政道路的交叉口分类进行介绍,分析各类交叉口的通行能力,对交叉口的交通路径优化方法进行分析。在此基础上,提出市政道路平面交叉口渠化设计策略,为改进城市交通组织方式、改善城市道路平面交叉口交通拥堵状况提供思路和方法。     

广西公路项目平交式工程安全评价探讨

文章介绍了公路项目平面交叉口工程安全评价的目的,分析了影响公路项目平面交叉口工程安全的因素,并以广西来马高速马山南互通出口与G210公路平交口项目为工程实例,从平纵线形、视距、交叉口间距、交通工程、施工方案等方面对公路项目平交式工程进行安全评价。     

基于潜在冲突量的交叉口安全评价方法研究

文章提出了潜在冲突量的概念,并对其进行了分类,通过车速、交通量、车道宽度等易获取的交通参数来推算交叉口潜在冲突量,引入混合交通当量,将潜在冲突量与混合交通当量比值作为交叉口安全评价的指标,并结合桂林市的9个交叉口进行了安全程度的评价。     

城市道路交叉口竖向设计方法及实例分析

文章介绍了道路平面交叉口竖向设计的原则和一般形式,阐述了常用的交叉口竖向设计方法及适用性,并结合工程设计实例,对比分析了两套拟定交叉口竖向设计方案的优缺点,得出最优方案,为今后城市道路交叉口竖向设计提供参考。     

南宁市白沙大桥北岸节点改造及其效果评价

文章以南宁市白沙大桥北岸节点改造设计为例,探讨城市道路平面交叉口改造设计的思路,同时从整体交通路网着眼,介绍采用交通仿真对改造效果进行评价的方法。     

交通冲突技术在桂林市交叉口安全评价中的应用

文章通过引入交通冲突的概念,以早高峰、晚高峰、平峰三时段的交通冲突量与混合交通当量比值作为交通安全评价的指标,利用灰色理论对桂林市九个典型交叉口进行安全程度的评价。     

基于大数据的交叉口信号控制系统设计

平面交叉口作为交通冲突的集中点,是制约当前城市道路交通通行能力的瓶颈。文章基于大数据技术,构建一体化交叉口信号处理系统,针对现有设施改善道路交通状况,为解决道路交通问题带来新的思路。     

交叉口左转交通流两种组织方式延误分析

左转交通流一直是城市道路交叉口中影响交叉口整体运行效率的关键,为了比较左转交通流不同组织方式对交叉口延误的影响,本文研究了专用相位左转和远引掉头左转两种左转交通组织方式下的车辆运行特性,并选取某典型交叉口为例进行基于Vissim的两种组织方式的实施效果评价。最终得出,在该交叉口情况下,采用远引掉头方式可明显减低车辆延误,提高交叉口运行效率。     

信控交叉口不同左转车道设置位置对交通安全的影响

城市道路信号干扰控制交叉口右侧处于与左转横向交通道路产生的信号冲突点最多,对车辆直行道和车流双向通行的信号干扰最大,使得城市平面道路交叉口左转交通信号延误程度增大。左转专用车道的交通设置使用方式主要分为两种:内置左转车道与外置左转车道。不同方向车道灯的布置及其形式对车辆左转方向交通的通行影响很大程度也会有所很大不同。本文通过实地调查,选取典型地区和交通重要路口情况进行模拟仿真实验分析,从转弯运行能力和通行能力的角度出发,探讨交叉口处不同左转车道的布置形式在不同交通特性下对整个交叉口的影响,从而明确其适用范围,为我国城市道路交通安全的发展提供参考。     

城市平面交叉口汽车排放优化策略研究

文章针对城市平面交叉口交通污染严重的问题,分析城市平面交叉口交通及行为特性、影响机动车排放的相关因素,从平面交叉口交通规划、交通控制二个方面阐述汽车排放优化措施。     

非灯控交叉口交通安全状况评价

非灯控交叉口是交通流中的节点,对非灯控交叉口的交通安全状况进行评价具有导向性意义。文章针对交叉口管控存在的问题,提出了交通安全状况评价原则和主要方法,阐述了非灯控交叉口交通安全的影响因素,并通过对沈阳市刘家窑十字交叉口进行交通安全状况评价,提出了具体的交叉口交通安全改善措施,以提高非灯控交叉口的交通安全性。     

Crash analysis at intersections in the CBD: A survival analysis model

Enhancing the safety level of urban roads especially in CBDs is paramount. Due to a large number of intersections in what is usually a grid road system in the CBDs, we investigate crashes occurring in and around an intersection. The question of interest in this study is: does the nature of crashes at intersections differ from those of the roads at midblock? Stated more precisely, considering the intersection as a reference point, does the distance to the reference point (i.e. midblock locations on the roads) correlate with different types of crashes compared to that of the intersection? A right answer can lead traffic engineers and safety auditors to propose different safety measures at intersections and the midblock locations. As a pilot study, we collected the last 9 years crash data of the CBD of Melbourne, Australia. For the first time, we employ Survival Analysis models -including Exponential, Weibull, and Log-logistic- to investigate a space-dependent phenomenon (i.e. accidents at proximity to the intersection). Of the outcome, highlights are: (i) police presence at busy intersections during busy night outs and weekends highly improves the pedestrian safety (ii) raised crossings at midblock locations lower likelihood of crashes of pedestrians as well as cars, (iii) lighting conditions at intersections must be watched and kept at a high level. (iv) Severity, likelihood, and location have no known association with the level of congestion. In other words, safety is first, always and everywhere. The results can be of interest to traffic authorities and policy makers in reinforcing traffic calming measures in the cities. The codes developed in this study are made available to the research community to be used in further studies.     

Traffic conflict models to evaluate the safety of signalized intersections at the cycle level

The safety of signalized intersections has often been evaluated at an aggregate level relating collisions to annual traffic volume and the geometric characteristics of the intersection. However, for many safety issues, it is essential to understand how changes in traffic parameters and signal control affect safety at the signal cycle level. This paper develops conflict-based safety performance functions (SPFs) for signalized intersections at the signal cycle level. Traffic video-data was recorded for six signalized intersections located in two cities in Canada. A video analysis procedure is proposed to collect rear-end conflicts and various traffic variables at each signal cycle from the recorded videos. The traffic variables include: traffic volume, maximum queue length, shock wave characteristics (e.g. shock wave speed and shock wave area), and the platoon ratio. The SPFs are developed using the generalized linear models (GLM) approach. The results show that all models have good fit and almost all the explanatory variables are statistically significant leading to better prediction of conflict occurrence beyond what can be expected from the traffic volume only. Furthermore, space-time conflict heat maps are developed to investigate the distribution of the traffic conflicts. The heat maps illustrate graphically the association between rear-end conflicts and various traffic parameters. The developed models can give insight about how changes in the signal cycle design affect the safety of signalized intersections. The overall goal is to use the developed models for the real-time optimization of signalized intersection safety by changing the signal design.     

Disaggregate safety evaluation for signalized intersections and evaluation tool

This study was to evaluate traffic safety of four‐legged signalized intersections and to develop a spreadsheet tool for identifying high‐risk intersections taking into consideration vehicle movements, left‐turn signal phase types, and times of day. The study used data from Virginia and employed count data models and the empirical Bayes (EB) method for safety evaluation of such intersections. It was found that crash pattern defined by vehicle movements involved in a crash and time of day are important factors for intersection crash analysis. Especially for a safety performance function (SPF), a model specification (Poisson or NB), inclusion of left‐turn signal types, type of traffic flow variables, variable functional forms, and/or magnitudes of coefficients turned out to be different across times of day and crash patterns. The spreadsheet application tool was developed incorporating the developed SPFs and the EB method. As long as Synchro files for signal plans and crash database are maintained, no additional field data collection efforts are required. Adjusting the developed SPFs and the spreadsheet for recent traffic and safety conditions can be done by applying the calibration methods employed in the SafetyAnalyst software and the Highway Safety Manual. Implementing the developed tool equipped with streamlining data entry would greatly improve accuracy and efficiency of safety evaluation of four‐legged signalized intersections in localities and highway agencies that cannot operate the SafetyAnalyst. Copyright © 2010 John Wiley & Sons, Ltd.     

Optimal distance between two branches of uncontrolled split intersection

This work examines the possibility of splitting an uncontrolled “X” intersection into two adjacent uncontrolled “T” intersections. This splitting aims to improve both the movement and safety of traffic. The problem addressed in this work is how to determine the optimal distance between the two adjacent T intersections. The best type of split, based on previous studies, is the one in which vehicles approach first the right turn and then the left turn in both directions of travel. The main conclusions drawn in this work refer to this preferred type. The optimal distance is arrived at on the basis of an objective function of minimal delay subject to blocking queues, passing (another vehicle) probabilities, budget limitations and safety threshold. The input data consist of 12 traffic volumes associated with all the traffic movements of an X intersection. The main findings are: (a) under a medium level of traffic volume, the blocking queue lengths are of the order of hundreds of meters and are very sensitive to the increase of volume toward and beyond saturation flow; (b) the passing probability function along the road segment between the two adjacent T intersections increases with the length of the segment and stabilizes at a length of a few hundred meters; (c) there is a relationship between accident frequency (accident rate and density) and the distance between the split intersections. An example of this relationship is introduced; and (d) the optimal distance between the two adjacent T intersections is found not only theoretically, but also practically for possible implementations.     

A driving force model for non-strict priority crossing behaviors of right-turn drivers

At urban intersections, conflicts between right-turn vehicles and through non-motorized vehicles are a critical cause of traffic congestion and safety challenges. Based on the fact that in different countries there is no strict priority in conflicts between motorized and non-motorized vehicles, this study focused on analysis of the inherent mechanism of this universal phenomenon. By the analogy of a force model for moving vehicles, this paper developed a micro driving force model, including the safety driving force and efficiency driving force, for right-turn drivers which constitute the dominant party during the non-strict priority crossing process. We further demonstrate that the strict priority crossing behavior is a special case of the proposed driving force model. All the parameters used in this model were calibrated through field data collected at twelve signalized intersection sites in Shanghai. Model validation results proved the accuracy and reliability of the proposed driving force model. The model was further proved that it can be used for right-turn vehicle's average crossing speed prediction. The sensitivity analysis identified the influence of vehicle type, non-motorized traffic flow rate, and non-motorized traffic speed on the average speed, and offered support for the rationality of the non-strict priority.     

A continuous-flow-intersection-lite design and traffic control for oversaturated bottleneck intersections

Oversaturation has become a severe problem for urban intersections, especially the bottleneck intersections that cause queue spillover and network gridlock. Further improvement of oversaturated arterial traffic using traditional mitigation strategies, which aim to improve intersection capacity by merely adjusting signal control parameters, becomes challenging since exiting strategies may (or already) have reached their “theoretical” limits of optimum. Under such circumstance, several novel unconventional intersection designs, including the well-recognized continuous flow intersection (CFI) design, are originated to improve the capacity at bottleneck intersections. However, the requirement of installing extra sub-intersections in a CFI design would increase vehicular stops and, more critically, is unacceptable in tight urban areas with closed spaced intersections. To address these issues, this research proposes a simplified continuous flow intersection (called CFI-Lite) design that is ideal for arterials with short links. It benefits from the CFI concept to enable simultaneous move of left-turn and through traffic at bottleneck intersections, but does not need installation of sub-intersections. Instead, the upstream intersection is utilized to allocate left-turn traffic to the displaced left-turn lane. It is found that the CFI-Lite design performs superiorly to the conventional design and regular CFI design in terms of bottleneck capacity. Pareto capacity improvement for every traffic stream in an arterial system can be achieved under effortless conditions. Case study using data collected at Foothill Blvd in Los Angeles, CA, shows that the new design is beneficial in more than 90% of the 408 studied cycles. The testing also shows that the average improvements of green bandwidths for the synchronized phases are significant.     

A programmable calculation procedure for number of traffic conflict points at highway intersections

Traffic movement conflict points at intersections are the points at which traffic movements intersect (including crossing, merging, and diverging). Numbers and distribution of different types of conflict points are used to evaluate intersection access management designs and safety performance. Traditionally, the determination of the numbers of conflict points for different traffic movements is based on manual methods, which causes the difficulty for computerized procedures to evaluate safety performance of different access management designs. Sometimes, a programmable calculation procedure may provide more effective solutions as compared with manual methods. This paper presents a programmable calculation procedure for the determination of the numbers of conflict points, which could be used as a basis for a computerized procedure. Concepts of virtual movement lanes and intersection quadrants are introduced to specify types of intersections, traffic lane configurations, and traffic movement regulations. Calculation models, based on such concepts, for traffic movement conflict points at signalized and unsignalized intersections can be obtained. In support of the procedure, case studies are presented in the paper. The procedure presented in the paper can be programmed into a computer program for the purpose of a computerized evaluation of intersection safety and design performance of different access management or control approaches. Copyright © 2012 John Wiley & Sons, Ltd.