信号交叉口安全评价及时空特性分析

为研究信号交叉口机动车冲突,对机动车驾驶人心理、行为特征进行分析。基于交叉口事故样本的静态数据、交通量和交通冲突数据为动态数据运用FKM聚类法对交叉口安全性进行评估。在此基础上研究交叉口机动车冲突分析时空特性,发现不同交叉口时间、空间冲突特征存在高度相关性和相似性;高峰时段冲突严重度和高峰时段、高峰小时流量存在线性关系并呈反比例关系;机动车冲突在不同空间上的危险度存在差异,其中直行与对向左转冲突危险度最高。     

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。     

基于交通冲突技术的高速公路合流区段安全性研究

为研究高速公路合流区段的安全性,本文以四川省境内高速公路为例对典型合流区段的交通冲突特性展开研究。选用PET作为评价指标并将交通冲突划分为3个等级:潜在冲突、轻微冲突、严重冲突。通过建立有序Logistic模型来探索影响冲突严重程度的显著性因素。结果表明:交织区交通流量、冲突车辆的速度差和二次冲突是增加冲突严重性的主要诱因;加速车道长度、规范的标志标线是保护因素;重型车辆比例对冲突严重程度影响呈非线性关系。     

城市轨道交通客流高峰传播影响研究

本文在总结城市轨道交通客流高峰特点的基础上,首次对城市轨道交通客流高峰传播的概念进行了定义,通过对城市轨道客流高峰传播机理的探讨,详细分析了城市轨道交通客流高峰传播造成的影响,并给出了度量客流高峰传播影响的主要内容。     

交通仿真在道路安全评价中的应用

我国道路交通的安全问题由于其严重程度的加剧正越来越受到人们的关注,因此,对于道路安全性的评价非常必要.事故统计方法和交通冲突方法是现在应用较多的道路安全评价方法,但这两种方法都存在着一定的不足.鉴于此,提出了一种基于交通仿真的道路安全评价方法并用一个范例介绍了应用交通仿真对道路进行安全性评价的基本过程.     

基于时空消耗模型的城市轨道交通承载力评价：以北京市为例

为监测城市轨道交通系统的供需矛盾及其时空差异化特征，引入时空消耗模型，分别以运输服务时空资源总量、出行需求时空资源占用量以及二者比值，计算了城市轨道交通供给能力、出行需求量和交通承载力。按照总体水平和均衡程度两个维度，选取轨道线网交通承载力、线网承载不均衡度和线网承载空间差异性作为城市轨道交通承载力评价指标，为更加精准地识别城市轨道交通出行需求与供给时空资源匹配关系提供支撑。实证研究结果表明：轨道线网供给能力总体高于出行需求量，全天轨道线网交通承载力位于高值区间，并呈现早晚高峰和午间小高峰的特征；线网承载力不均衡度显著偏高，轨道站间区段交通承载力差距悬殊，但在空间上总体呈现显著离散特征。     

国外机场陆侧交通流特性分析

由于航空枢纽的特殊性,其陆侧交通特性与其他交通枢纽周边交通特性有着很大的差别,机场陆侧交通特性分析是网络规划的关键与基础性问题。本文从交通流的类别、分布以及高峰时间三个方面,对机场陆侧交通的特性进行了较为详细的分析。     

大型活动的交通调查及分析

随着我国经济的不断发展,全国各地举行的大型活动越来越多。大型活动产生突增交通量造成周边地区的交通拥挤,而分析大型活动带来的交通拥挤则是以对大型活动的交通调查为基础的。以长春市南岭体育场周围的道路交通系统为基础,对举行足球比赛产生的观众到达高峰和离开高峰进行了实地调查,并通过问卷的方式对观众出行方式及其他与此活动相关的特性进行了分析。     

潮汐车道实施效果及影响——北京市紫竹院路为例

以北京市紫竹院路为例,对比紫竹院路潮汐车道实施前后的交通调查数据,论证了紫竹院路设置潮汐车道的必要性和可行性,从交通流量、交通出行效率和设施利用率三个方面分析潮汐车道的实施效果,以及其对周边路网流量分布情况的影响。研究结果表明,潮汐车道开通后,紫竹院路进城、出城方向的高峰小时交通量显著增加,行程车速大幅提高,单车道利用率随着断面交通流量增加趋向均衡,路段交通出行环境改善;紫竹院路周边主要平行道路的高峰小时流量基本保持不变,潮汐车道可能会引起更远范围路网交通流量的重新分布,以达到新的交通平衡状态。     

向多核演变期带形城市的交通特征

带形城市发展期带状特征凸显,通过大量的参数类比得出,由单核向多核发展这一特殊发展期的交通特征:老核心区原有用地模式调整难,高峰时易发生交通拥堵;城市带向发展拉大了出行距离,居民的出行次数、出行距离和平均出行时间均会显著增加;新核心区发展初期,交通需求仍主要集中在老核心发展成熟区内;伴随新核心区发展,核心区之间的出行需求量快速增大,新老核心间轴向干道会集中大量交通,高峰时交通压力过大;新区发展逐步成熟后,新老核心区间联系会更密切,新核心内部出行增大。     

Assessing energy consumption impacts of traffic shifts based on real-world driving data

Information and communication technologies used for on-board vehicle monitoring have been adopted as an additional tool to characterize mobility flows. Furthermore, traffic volumes are traditionally measured to understand cities traffic dynamics. This paper presents an innovative methodology that uses an extensive and complementary real-world dataset to make a scenario-based analysis allowing assessing energy consumption impacts of shifting traffic from peak to off-peak hours. In the specific case of the city of Lisbon, a sample of 40 drivers was monitored for a period of six months. The obtained data allowed testing the impacts of increasing the percentage of traffic shifting from peak to off-peak hours in energy consumption. Both average speed and energy consumption variations were quantified for each of the tested percentages, allowing concluding that for traffic shifts of up to 30% a positive impact in consumption can be observed. In terms of potential gains associated to shifting traffic from peak hours, reductions in energy consumption from 0.1% to 0.4% can be obtained for traffic volumes shifts from 5 to 30%. Overall, the maximum reduction in energy consumption is achieved for a 20% traffic shift. Average speed variation follows the same trend as energy consumption, but in the opposite direction, i.e. instead of decreasing, average speed increases. For the best case scenario, considering only the sections of roads with traffic sensors, a 1.4% reduction in trip time may be achieved, as well as savings of up to 6 l of fuel and 14.5 kg of avoided CO₂ emissions per day.     

Modelling traffic flows and estimating road travel times in transportation network under dynamic disturbances

Transportation - Traffic congestion is a common phenomenon in road transportation networks, especially during peak hours. More accurate prediction of dynamic traffic flows is very important for...     

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.     

Crossing the bridge: The effects of time-varying tolls on curbing congestion

This paper estimates the traffic volume and travel time effects of the road congestion pricing implemented on the San Francisco-Oakland Bay Bridge. I employ both difference-in-differences and regression discontinuity approaches to analyze previously unexploited data for the two years spanning the price change and obtain causal estimates of the hourly average treatment effects of the policy. I find evidence of peak spreading in traffic volume and decreases in travel time during peak hours. I also find suggestive evidence of substitution to a nearby bridge and decreases in travel time variability. In addition, I calculate own- and cross-price elasticities.     

Real-time route diversion control in a model predictive control framework with multiple objectives: Traffic efficiency,emission reduction and fuel economy

In this paper, the route recommendation provided by the traffic management authority, rather than the uncontrollable bifurcation splitting rate, is directly considered as the control variable in the route guidance system; a real-time en-route diversion control strategy with multiple objectives is designed in a Model Predictive Control (MPC) framework with regard to system uncertainties and disturbances. The objectives include not only traffic efficiency, but also emission reduction and fuel economy, which respectively correspond to minimizing the total time spent (TTS), total amount of emissions and fuel consumption for all vehicles moving through a network. In the MPC framework, the routing control problem is transformed to be a constrained combinational optimization, which is solved by the parallel Tabu Search algorithm. Two representative traffic scenarios are tested, and the simulation results show: (1) The room for improvement in each objective by means of route diversion control is not consistent with each other and varies with the utilized traffic scenario. In the peak hour, the routing control can lead to significant improvements in TTS and fuel economy, while a relatively small improvement in emission reduction is achieved; in the off-peak hour, however, it is opposite, which indicates that routing is possibly dispensable from the aspect of improving traffic efficiency, but is required from the aspect of emission reduction. (2) The conflict among the multiple objectives varies with the utilized traffic scenario in route diversion control. Improving traffic efficiency often conflicts with emission reduction in both scenarios. For the objectives of traffic efficiency and fuel economy, they are not conflicting in peak hour, while in the off-peak hour, the two objectives are likely conflicting, and the improvement in one objective can lead to the degradation in the other objective. (3) Regardless of the scenarios of peak hour or off-peak hour, the proposed control strategy can result in a proper trade-off among the three chosen objectives.     

Multi‐level traffic control at large four‐leg roundabouts

Yield control and full signalization are typical traffic control solutions that can be used at large roundabouts. In the face of increasing congestion issues, it is preferred to use yield control during off‐peak periods and full signalization during peak periods. To automatically accommodate time‐varying vehicular demands, a multi‐level traffic control (MTC) is developed to implement hybrid yield control and fully actuated control at large four‐leg roundabouts. With new application of traffic control devices and traffic detection system, the right‐of‐way can be assigned to entering and circulating vehicles in three modes. The ‘all entering’ mode is equivalent to a yield control. The ‘no entering’ and ‘concurrent entering’ modes are equivalent to a fully actuated control. On the basis of time headways and occupancy times that are detected on the entry and circulatory roadways, the mode of right‐of‐way assignment can be changed in response to actual traffic conditions. For a specific mode of right‐of‐way assignment, traffic signal operation is managed by some detectable traffic events that are happening. The results of the simulation experiments conducted by VISSIM indicated that: (i) MTC was stabilized at the ‘all entering’ mode during off‐peak periods and at the ‘concurrent entering’ mode during peak periods; (ii) MTC would typically change the mode of right‐of‐way assignment according to actual traffic conditions as vehicular demands increased from off‐peak to peak or decreased from peak to off‐peak; and (iii) statistically speaking, MTC inherited the operational advantages of yield control and fully actuated control, and could be effective in improving the operational performance of large four‐leg roundabouts for all hours of the day, regardless of the level of left‐turn ratios. Copyright © 2016 John Wiley & Sons, Ltd.     

Developing evasive action‐based indicators for identifying pedestrian conflicts in less organized traffic environments

There has been a growing interest in using surrogate safety measures such as traffic conflicts to analyse road safety from a broader perspective than collision data alone. This growing interest has been aided by recent advances in automated video‐based traffic conflict analysis. The automation enables accurate calculation of various conflict indicators such as time‐to‐collision and post‐encroachment time. These indicators rely on road users getting within specific temporal and spatial proximity from each other and therefore assume that proximity is a surrogate for conflict severity. However, this assumption may not be valid in many driving environments where close interactions between road users are common. The objective of this paper is to investigate the applicability of time proximity conflict indicators for evaluating pedestrian safety in less‐organized traffic environments with a high mix of road users. Several alternative behavioural conflict indicators based on detecting pedestrian evasive actions are recommended to better measure traffic conflicts in such traffic environments. These indicators represent variations in the spatio‐temporal gait parameters (step length, step frequency and walk ratio) immediately before the conflict point. A highly congested shared intersection in Shanghai, China, with frequent pedestrian conflicts is used as a case study. Traffic conflicts are analysed with the use of automated video‐based analysis techniques. The results showed that evasive action‐based indicators have higher potential to identify pedestrian conflicts and measure their severity in high mix less organized traffic environments than time proximity measures such as time‐to‐collision and post‐encroachment time. Copyright © 2016 John Wiley & Sons, Ltd.     

Real-time energy-efficient traffic control via convex optimization

This article proposes a macroscopic traffic control strategy to reduce fuel consumption of vehicles on highways. By implementing Greenshields fundamental diagram, the solution to Moskowitz equations is expressed as linear functions with respect to vehicle inflow and outflow, which leads to generation of a linear traffic flow model. In addition, we build a quadratic cost function in terms of vehicle volume to estimate fuel consumption rate based on COPERT model. A convex quadratic optimization problem is then formulated to generate energy-efficient traffic control decisions in real-time. Simulation results demonstrate significant reduction of fuel consumption on testing highway sections under peak traffic demands of busy hours.     

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.