The kinematic wave model with finite decelerations: A social force car-following model approximation

This paper derives a five-parameter social force car-following model that converges to the kinematic wave model with triangular fundamental diagram. Analytical solutions for vehicle trajectories are found for the lead-vehicle problem, which exhibit clockwise and counter-clockwise hysteresis depending on the model’s parameters and the lead vehicle trajectory. When coupled with a stochastic vehicle dynamics module, the model is able to reproduce periods and amplitudes of stop-and-go waves, as reported in the field. The model’s stability conditions are analysed and its trajectories are compared to real data.     

Connected vehicle penetration rate for estimation of arterial measures of effectiveness

The Connected Vehicle (CV) technology is a mobile platform that enables a new dimension of data exchange among vehicles and between vehicles and infrastructure. This data source could improve the estimation of Measures of Effectiveness (MOEs) for traffic operations in real-time, allowing to perfectly monitor traffic states after being fully adopted. However, as with any novel technology, the CV adoption will be a gradual process. This research focuses on determining minimum CV technology penetration rates that would guarantee accurate MOE estimates on signalized arterials. First, we present estimation methods for various MOEs such as average speed, number of stops, acceleration noise, and delay, followed by an initial assessment of the penetration rates required to accurately estimate them in undersaturated and oversaturated conditions. Next, we propose a methodology to determine the minimum CV market penetration rates to guarantee accurate MOE estimates as a function of traffic conditions, signal settings, sampling duration, and the MOE variability. A correction factor is also provided to account for small vehicle populations where sampling is done without replacement. The methodology is tested in a simulated segment of the San Pablo Avenue arterial in Berkeley, CA. The outcomes show that the minimum penetration rate required can be estimated within 1% for most MOEs under a wide range of traffic conditions. The proposed methodology can be used to determine if MOE estimates obtained with a portion of CV equipped vehicles can yield accurate enough results. The methodology could also be used to develop and assess control strategies towards improved arterial traffic operations.     

On some experimental features of car-following behavior and how to model them

We have carried out car-following experiments with a 25-car-platoon on an open road section to study the relation between a car’s speed and its spacing under various traffic conditions, in the hope to resolve a controversy surrounding this fundamental relation of vehicular traffic. In this paper we extend our previous analysis of these experiments, and report new experimental findings. In particular, we reveal that the platoon length (hence the average spacing within a platoon) might be significantly different even if the average velocity of the platoon is essentially the same. The findings further demonstrate that the traffic states span a 2D region in the speed-spacing (or density) plane. The common practice of using a single speed-spacing curve to model vehicular traffic ignores the variability and imprecision of human driving and is therefore inadequate. We have proposed a car-following model based on a mechanism that in certain ranges of speed and spacing, drivers are insensitive to the changes in spacing when the velocity differences between cars are small. It was shown that the model can reproduce the experimental results well.     

Can Hong Kong price-manage its cross-harbor-tunnel congestion?

Hong Kong drivers face daily congestion, especially at the Cross Harbor Tunnel (CHT) whose tolls are substantially lower than those of the drivers’ other two tunnel options: the Eastern Harbor Crossing (EHC) and the Western Harbor Crossing (WHC). In 2013, the Hong Kong Special Administrative Region (HKSAR) Government issued a consultation paper, seeking public comments on three toll-change proposals that would raise the CHT’s tolls and lower the EHC’s tolls. The WHC’s tolls would remain unchanged due to its congested connecting roads. Using monthly crossing data available from the HKSAR’s Transport Department for 2000–2012, this paper uses a Generalized Leontief demand system to document that the usage patterns of the three tunnels is price-responsive. Hence, we conclude that the proposed toll changes are likely to be effective in transportation demand management, by shifting a portion of the CHT’s usage to the EHC and WHC, thereby relieving the CHT’s congestion.     

减压环在被动柔性防护网中的耗能作用研究

基于落石防护措施受力系统的复杂性及不同系统参数研究的有效性角度考虑,数值方法正成为研究被动柔性防护网动态受力行为的重要手段。为研究被动柔性防护网中的减压环在落石冲击作用下的耗能及缓冲作用,以实际被动柔性防护网为原型,建立含减压环及不含减压环的两种被动柔性防护网有限元模型,基于ANSYS/LSDYNA分析两种防护网在不同冲击能量及冲击位置下的动力响应。研究结果表明:减压环可增强被动柔性防护网的柔性、改善作用部位的性能,同时能显著地提高被动柔性防护网的耗能能力。同时,数值结果的对比分析为下一步试验设计以校正有限元模型和研究实体构件受力特征提供了参考依据。     

Real time traffic flow outlier detection using short-term traffic conditional variance prediction

Outliers in traffic flow series represent uncommon events occurring in the roadway systems and outlier detection and investigation will help to unravel the mechanism of such events. However, studies on outlier detection and investigations are fairly limited in transportation field where a vast volume of traffic condition data has been collected from traffic monitoring devices installed in many roadway systems. Based on an online algorithm that has the ability of jointly predict the level and the conditional variance of the traffic flow series, a real time outlier detection method is proposed and implemented. Using real world data collected from four regions in both the United States and the United Kingdom, it was found that outliers can be detected using the proposed detection strategy. In addition, through a comparative experimental study, it was shown that the information contained in the outliers should be assimilated into the forecasting system to enhance its ability of adapting to the changing patterns of the traffic flow series. Moreover, the investigation into the effects of outliers on the forecasting system structure showed a significant connection between the outliers and the forecasting system parameters changes. General conclusions are provided concerning the analyses with future work recommended to investigate the underlying outlier generating mechanism and outlier treatment strategy in transportation applications.     

AIS在海上交通调查中的应用

摘要:海上交通调查的基本目的是采用一切有效手段收集海上交通的基本数据并随之进行统计分析和理论研究,以便从宏观上和微观上掌握和了解海上交通的实际状况、基本特征和一般规律。通常所说的海上交通调查主要指交通观测。随着船舶自动识别系统(AIS)的诞生和完善,传统交通观测方法的弊端暴露无遗。通过对海上交通观测的新老方法的分析比较,提出了AIS在海上交通调查过程中需要解决的技术问题,并结合宁波虾峙门的实地观测进行了具体的应用。     

自发电用60kW双频变频发电机的设计和使用

介绍了自发电用60 kW双频变频发电机的结构、工作状态和励磁系统的设计     

直压式废弃物转运车举升机构的优化设计

通过对直压式废弃物转运车举升机构的力学分析,建立了举升机构的数学模型,运用MATLAB数值计算方法,完成了举升机构的技术参数优化设计,从而提高了举升机构的使用性能。     

运用模糊理论建立渡船安全评价体系

渡船安全一直是长江水上交通安全监管的重点和难点。文中总结提炼渡船安全管理的经验、措施和做法,运用模糊数学和层次分析法,探索建立渡船安全评价体系的新途径。