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。     

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。     

我国交通运输业碳排放分析

2030年我国将实现二氧化碳排放达峰目标,交通运输业是主要的碳排放源之一,随着经济社会发展,客货运输需求持续增长,交通运输业碳排放在总排放中的比重将持续增加。本文测算了我国非营运车辆碳排放量,在同一口径下对比了中外交通运输业碳排放情况,研究了我国交通运输业碳排放发展趋势,分析了我国交通运输业碳排放达峰时间和达峰比例。本文的研究对我国采取有效措施控制交通运输业碳排放,实现国家碳排放达峰目标具有重要意义。     

建制部队战略投送保障需求测算方法研究

建制部队战略投送保障需求的测算是一项重大而又艰巨的任务。针对目前投送保障需求测算方法缺乏规范性和统一性问题,提出战略投送保障需求测算方法框架。通过分析建立战略投送保障任务模型和需求模型,给出任务-需求匹配测算方法。以铁路车辆保障为例,构建人员和装备的保障需求测算模型。通过该方法的研究,为整建制部队战略投送保障方案、能力评估、技术装备与标准规范等研究提供设计参考,为整建制部队战略投送保障能力建设提供决策指导。     

基于动态停车视距测算的山地城市道路平面设计优化研究

本文考虑行车过程中制动时间组成及影响因素,基于车辆弯道行驶轨迹线的几何三角函数,结合车辆动态行车视距修正系数及Matlab程序建立动态停车视距模型;以重庆十八梯片区厚慈街95号交叉口道路节点进行方案论证及优化。结果表明：结合车辆行驶轨迹线中的几何与设计参数,基于动态停车视距测算算法可输出动态停车视距线段端点坐标值以实现视距的可视化与可测量化;基于动态停车视距模型的视距计算值与规范值的最大误差率为12.45%,且优化规划道路前后的计算值均大于规范值,证实了该视距测算模型的可行性与适用性,研究结果为山地城市风貌保护区内道路停车视距的平面设计优化提供一种新的解决思路。     

公路交叉口交通工程设施优化设计研究

公路交叉口交通工程设施优化设计,能够有效缓解公路运输压力,降低公路交通安全事故发生率,推进我国交通事业安全发展。基于此,以公路交叉口交通工程设施为研究对象,分析优化设计的必要性及原则,并从交叉口控制方式、交叉口车道、交通标志、路线改线等方面提出优化设计思路,以期为相关从业人员提供参考。     

燃气管道泄漏和置换放散研究

文中从影响管道泄漏的因素出发,列举了国内外相关研究成果,包括研究较少的因素。介绍了管道置换放散的工程实例,总结现场经验,减少对空排放量,并提出研究放散量精确计算的方法,为测算甲烷漏排量提供参考。     

越江盾构隧道全寿命期碳排放特征与减排途径研究

越江隧道是城市网络中的重要交通基础设施，也是城市交通碳排放主要来源之一，对越江隧道的碳排放计量、评估与减排机制进行研究十分必要。首先确定越江隧道全寿命期碳排放计量边界和清单，分为物化阶段和运维阶段两部分。基于清单分析，建立以碳排放因子法为基础的越江盾构隧道全寿命期碳排放计量模型，并系统分析越江隧道全寿命期与工程活动的对应关系，提出绿色技术驱动的越江隧道碳减排效应估算流程，以碳减排效应系数表征绿色技术的碳排放效果。研究表明：国内外对各类绿色技术的碳减排效应量化研究严重不足；在物化阶段，盾构隧道单位碳排放量随直径的增大而增大，在材料和结构设计不发生变革的情况下，物化阶段碳减排潜力有限；在运维阶段，机电设施的碳排放量与物化阶段碳排放量基本相当，从全寿命期考虑，运维阶段碳减排潜力及可控性更大。     

道路交通碳排放测算方法研究综述

碳排放会给环境带来较大的影响，而评估碳排放的基础是对不同尺度下的碳排放量进行准确的测算。根据IPCC的国家温室气体清单指南，移动源碳排放计算方法可以分为自上而下模型和自下而上模型。本文以此为依据，对近十年来道路交通碳排放测算方法的相关研究进行归纳和总结，并在此基础上提出了不同场景下道路交通碳排放测算方法选择应该考虑的因素，最后对未来道路交通碳排放测算方法的改进进行了展望。     

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。     

Evaluating effects of traffic and vehicle characteristics on vehicular emissions near traffic intersections

Urban air quality is generally poor at traffic intersections due to variations in vehicles’ speeds as they approach and leave. This paper examines the effect of traffic, vehicle and road characteristics on vehicular emissions with a view to understand a link between emissions and the most likely influencing and measurable characteristics. It demonstrates the relationships of traffic, vehicle and intersection characteristics with vehicular exhaust emissions and reviews the traffic flow and emission models. Most studies have found that vehicular exhaust emissions near traffic intersections are largely dependent on fleet speed, deceleration speed, queuing time in idle mode with a red signal time, acceleration speed, queue length, traffic-flow rate and ambient conditions. The vehicular composition also affects emissions. These parameters can be quantified and incorporated into the emission models. There is no validated methodology to quantify some non-measurable parameters such as driving behaviour, pedestrian activity, and road conditions     

Modal analysis of real-time,real world vehicular exhaust emissions under heterogeneous traffic conditions

This study presents the characteristics of real world, real time, on-road vehicular exhaust emission namely, carbon monoxide (CO), nitric oxide (NO), hydrocarbons (HC), and carbon dioxide (CO₂) emitted under heterogeneous traffic conditions. Field experiments were performed on major category of vehicles in developing countries, i.e. two-wheelers, auto-rickshaws, cars and buses. The on-board monitoring was carried out on different corridors with varying road geometry. Results revealed that the driving cycle was dependent on the road geometry, with two lane mixed flow corridor having lot of short term events compared to that of arterial road. Vehicular emissions during idling and cruising were generally low compared to emissions during acceleration. It was also found that emissions were significantly dependent on short term events such as rapid acceleration and braking during a trip. Also, the standard emission models like COPERT and CMEM under predicted the real world emissions by 30–200% depending upon different driving modes. The on-road emissions measurements were able to capture the emission characteristics during the micro events of real world driving scenarios which were not represented by standard vehicle emission measured at laboratory conditions.     

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.     

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。     

A traffic noise model for road intersections in the city of Cartagena de Indias,Colombia

Road traffic noise models are fundamental tools for designing and implementing appropriate prevention plans to minimize and control noise levels in urban areas. The objective of this study is to develop a traffic noise model to simulate the average equivalent sound pressure level at road intersections based on traffic flow and site characteristics, in the city of Cartagena de Indias (Cartagena), Colombia. Motorcycles are included as an additional vehicle category since they represent more than 30% of the total traffic flow and a distinctive source of noise that needs to be characterized. Noise measurements are collected using a sound level meter Type II. The data analysis leads to the development of noise maps and a general mathematical model for the city of Cartagena, Colombia, which correlates the sound levels as a function of vehicle flow within road intersections. The highest noise levels were 79.7 dB(A) for the road intersection María Auxiliadora during the week (business days) and 77.7 dB(A) for the road intersection India Catalina during weekends (non-business days). Although traffic and noise are naturally related, the intersections with higher vehicle flow did not have the highest noise levels. The roadway noise for these intersections in the city of Cartagena exceeds current limit standards. The roadway noise model is able to satisfactorily predict noise emissions for road intersections in the city of Cartagena, Colombia.     

Urban real-world driving traffic emissions during interruption and congestion

On-road emissions from urban traffic during interrupted and congested flow conditions are too high as compared to free-flow condition and often influenced by accelerating and decelerating speed due to frequent stop-and-go. In this study, we measured emissions from passenger cars and auto-rickshaws during peak and off-peak hours and analyzed according to different mileages with the instantaneous speed and acceleration for interrupted and congested traffic conditions. It was found that during flow, several short-events lasting over fractions of a second each lead to a sharp increase in pollutant emissions, indicating episodic conditions. The emission levels are sensitive to frequency and intensity of acceleration and deceleration, in accordance with the traffic-flow patterns and speed, besides mileages. Further, congestion conditions occur during both peak and off-peak hours, but last for different durations. The results are important in the sense that instantaneous estimates of pollutant emissions are necessary for the assessment of air quality in urban centers and for an effective traffic management plan.     

Mobility and environment improvement of signalized networks through Vehicle-to-Infrastructure (V2I) communications

Traffic signals, even though crucial for safe operations of busy intersections, are one of the leading causes of travel delays in urban settings, as well as the reason why billions of gallons of fuel are burned, and tons of toxic pollutants released to the atmosphere each year by idling engines. Recent advances in cellular networks and dedicated short-range communications make Vehicle-to-Infrastructure (V2I) communications a reality, as individual cars and traffic signals can now be equipped with communication and computing devices. In this paper, we first presented an integrated simulator with V2I, a car-following model and an emission model to simulate the behavior of vehicles at signalized intersections and calculate travel delays in queues, vehicle emissions, and fuel consumption. We then present a hierarchical green driving strategy based on feedback control to smooth stop-and-go traffic in signalized networks, where signals can disseminate traffic signal information and loop detector data to connected vehicles through V2I communications. In this strategy, the control variable is an individual advisory speed limit for each equipped vehicle, which is calculated from its location, signal settings, and traffic conditions. Finally, we quantify the mobility and environment improvements of the green driving strategy with respect to market penetration rates of equipped vehicles, traffic conditions, communication characteristics, location accuracy, and the car-following model itself, both in isolated and non-isolated intersections. In particular, we demonstrate savings of around 15% in travel delays and around 8% in fuel consumption and greenhouse gas emissions. Different from many existing ecodriving strategies in signalized road networks, where vehicles’ speed profiles are totally controlled, our strategy is hierarchical, since only the speed limit is provided, and vehicles still have to follow their leaders. Such a strategy is crucial for maintaining safety with mixed vehicles.     

Using connected vehicle technology to improve the efficiency of intersections

Information from connected vehicles, such as the position and speed of individual vehicles, can be used to optimize traffic operations at an intersection. This paper proposes such an algorithm for two one-way-streets assuming that only a certain percentage of cars are equipped with this technology. The algorithm enumerates different sequences of cars discharging from the intersection to minimize the objective function. Benefits of platooning (multiple cars consecutively discharging from a queue) and signal flexibility (adaptability to demand) are also considered. The goal is to gain insights about the value (in terms of delay savings) of using connected vehicle technology for intersection control.Simulations are conducted for different total demand values and demand ratios to understand the effects of changing the minimum green time at the signal and the penetration rate of connected cars. Using autonomous vehicle control systems, the signal could rapidly change the direction of priority without relying on the reaction of drivers. However, without this technology a minimum green time is necessary. The results of the simulations show that a minimum green time increases the delay only for the low and balanced demand scenarios. Therefore, the value of using cars with autonomous vehicle control can only be seen at intersections with this kind of demand patterns, and could result in up to 7% decrease in delay. On the other hand, using information from connected vehicles to better adapt the traffic signal has proven to be indeed very valuable. Increases in the penetration rate from 0% up to 60% can significantly reduce the average delay (in low demand scenarios a decrease in delay of up to 60% can be observed). That being said, after a penetration rate of 60%, while the delays continue to decrease, the rate of reduction decreases and the marginal value of information from communication technologies diminishes. Overall, it is observed that connected vehicle technology could significantly improve the operation of traffic at signalized intersections, at least under the proposed algorithm.     

A tool for calculating aircraft emissions and its application to Greek airspace

This paper quantifies the impact of aircraft emissions on local air quality and climate change. Aircraft emissions during the cruise cycle and the landing/take-off cycle are considered. A tool is developed that computes emission values using real-time air traffic data derived from various databases. Emissions include carbon dioxide, hydrocarbons, carbon monoxide and nitrogen oxides. The overall output is a detailed ‘emissions map’ of a given territory that enables the identification of critical emission spots including routes, airports, season, aircraft type and flight category. The method can be used for real-time monitoring of airline emissions and for policy analysis. The proposed tool and resulting outputs are illustrated in the case of the Greek airport system using domestic, international and overflights. Demand volatility driven mainly by tourism and its impact on emissions is assessed.     

Spatiotemporal intersection control in a connected and automated vehicle environment

Current research on traffic control has focused on the optimization of either traffic signals or vehicle trajectories. With the rapid development of connected and automated vehicle (CAV) technologies, vehicles equipped with dedicated short-range communications (DSRC) can communicate not only with other CAVs but also with infrastructure. Joint control of vehicle trajectories and traffic signals becomes feasible and may achieve greater benefits regarding system efficiency and environmental sustainability. Traffic control framework is expected to be extended from one dimension (either spatial or temporal) to two dimensions (spatiotemporal). This paper investigates a joint control framework for isolated intersections. The control framework is modeled as a two-stage optimization problem with signal optimization at the first stage and vehicle trajectory control at the second stage. The signal optimization is modeled as a dynamic programming (DP) problem with the objective to minimize vehicle delay. Optimal control theory is applied to the vehicle trajectory control problem with the objective to minimize fuel consumption and emissions. A simplified objective function is adopted to get analytical solutions to the optimal control problem so that the two-stage model is solved efficiently. Simulation results show that the proposed joint control framework is able to reduce both vehicle delay and emissions under a variety of demand levels compared to fixed-time and adaptive signal control when vehicle trajectories are not optimized. The reduced vehicle delay and CO₂ emissions can be as much as 24.0% and 13.8%, respectively for a simple two-phase intersection. Sensitivity analysis suggests that maximum acceleration and deceleration rates have a significant impact on the performance regarding both vehicle delay and emission reduction. Further extension to a full eight-phase intersection shows a similar pattern of delay and emission reduction by the joint control framework.