Predicting queue variability to enable analysis of overload risk

ABSTRACT

Predicting the risk of traffic demands and delays exceeding critical limits at road junctions, airports, hospitals, etc., requires knowing how both mean and variance of queue size vary over time. Microscopic simulation can explore variability but is computationally demanding and gives only sample results. A computationally efficient approximation to the mean is used in many modelling tools, but only empirical extensions for variance in particular situations have been available. The paper derives theoretical formulae for time-dependent and equilibrium variance, believed to be novel and to apply generally to queues covered by the Pollaczek–Khinchin mean formula, and offering possible structural insights. These are applied in an extended approximation giving mutually consistent mean and variance estimates with improved accuracy. Tests on oversaturated peak demand cases are compared with Markov probabilistic simulation, demonstrating accuracy (R^2?>?0.99) for typical random, priority-like (M/M/1) and traffic-signal-like (M/D/1) queues. Implications for risk analysis, planning and policy are considered.     

Risk assessment framework for exposure of cargo and ports to natural hazards and climate extremes

There is an increase in risks and catastrophic losses in maritime transport including ports and cargo. Significant losses have been associated with large scale natural hazards, such as earthquakes, tsunami, cyclones, and other extreme weather events. This paper identifies the main gaps in understanding maritime risks in transportation research. The gaps are attributed to insufficient empirical work available from the maritime transport and logistics research community to guide multi-risk and natural hazards impact assessment on seaport and cargo. In addition, disaster studies communities have barely made adequate efforts to understand and assess port and cargo risks arising from multi-hazards and disaster events. This paper examines existing conceptual frameworks concerning exposure and risk assessments of natural catastrophe’s impacts. Furthermore, the paper identifies trends and gaps in risk assessment frameworks in the field of disaster studies that can be beneficial for maritime risk research. The authors propose a new risk assessment framework that can guide future research and multi-hazard risk assessment processes at different scales of maritime risks.     

工程总承包模式下项目业主风险防范探讨

文章结合工程总承包的特点,分析了工程总承包模式下项目业主在项目实施过程中所面临的风险,提出了相应的防范风险的措施。     

高埋深软硬岩互层地质条件下敞开式TBM岩爆段施工方法研究

基于喜马拉雅山区域某软硬岩性互层地质条件下的深埋隧洞工程,为解决该区域TBM施工过程中的岩爆问题,统计分析了TBM施工过程中的岩爆特征;在施工过程中开展了多种岩爆规避试验,形成了一套较完整的有针对性的施工方法： 1）岩爆风险巡查常态化; 2）超前地质预报和超前处理措施相结合; 3）支护材料和支护方式合理化; 4）掘进参数动态调整。在后续的施工中加以应用,取得了较好的效果,可以为类似地质条件下的安全施工提供参考。     

Vehicle mass as a determinant of fuel consumption and secondary safety performance

One interaction between environmental and safety goals in transport is found within the vehicle fleet where fuel economy and secondary safety performance of individual vehicles impose conflicting requirements on vehicle mass from an individual’s perspective. Fleet characteristics influence the relationship between the environmental and safety outcomes of the fleet; the topic of this paper. Cross-sectional analysis of mass within the British fleet is used to estimate the partial effects of mass on the fuel consumption and secondary safety performance of vehicles. The results confirmed that fuel consumption increases as mass increases and is different for different combinations of fuel and transmission types. Additionally, increasing vehicle mass generally decreases the risk of injury to the driver of a given vehicle in the event of a crash. However, this relationship depends on the characteristics of the vehicle fleet, and in particular, is affected by changes in mass distribution within the fleet. We confirm that there is generally a trade-off in vehicle design between fuel economy and secondary safety performance imposed by mass. Cross-comparison of makes and models by model-specific effects reveal cases where this trade-off exists in other aspects of design. Although it is shown that mass imposes a trade-off in vehicle design between safety and fuel use, this does not necessarily mean that it imposes a trade-off between safety and environmental goals in the vehicle fleet as a whole because the secondary safety performance of a vehicle depends on both its own mass and the mass of the other vehicles with which it collides.     

信号交叉口行车风险场建立及车辆通行行为优化

随着汽车逐步向智能化、网联化发展,智能网联车辆逐步进入实际应用阶段。进行智能网联车辆的通行行为优化,对提升驾驶安全性和行车效率,避免事故发生和交通拥堵至关重要。车辆在通过交叉口时将受到很多环境及运动因素的影响,而现有的通行优化模型难以准确表达各类因素共同作用下的行驶环境。为此,基于风险场理论建立由环境场和运动场组成的信号交叉口行车风险场,表征信号交叉口中每点的实时行车风险程度,从而引导车辆驶向风险值低点,并提供下一步长的位移及速度指引,实现车辆的动态轨迹优化及速度控制。典型场景下的仿真结果表明：在优化模型的控制下单车的信号交叉口通行效率明显提升,其中直行方向车辆单车平均通行效率提升最高,平均提升6.35%,通过对交叉口面积内所有车辆进行通行行为优化,交叉口通行效率提升了9.3%,这表明所建模型可以准确表达交叉口行车环境并优化车辆通行行为。研究结论可应用于自动驾驶车辆的交叉口通行控制,并为网联环境下的行车环境表达和安全驾驶控制提供模型基础。     

管道主要风险的失效频率数据分析

对其他国家地区管道运输发展中管道所发生的事故进行研究,尝试对一些事故报告数据进行分析,研究它们的特性.借鉴其他管道系统的事故原因,列出了管道类型初步分类应考虑的条件和面临的主要风险.认为对管道类别应该有区别地划分.     

船上实施听力保护的技术要求及应用

船舶噪声对船员的听力损伤是众所周知的,甚至发生部分船员的永久性听力损失。国际海事组织第91届海安会通过了新的《船上噪声等级规则》,围绕实施噪声规则,分析了听力保护的技术要求和正确选用听力保护器的技术依据,探讨了佩戴听力保护器对语言交流和感受听觉信号造成的影响。强调必须开展听力损伤的风险评估,并对识别听力损伤的特殊风险因素提出了建议。     

基于船舶领域和MMG的最晚施舵点/CRI研究

提出了一种基于MMG和船舶领域的LSP计算模型,以及改进的空间碰撞危险度（space collision risk index,SCRI）/时间碰撞危险度（time collision risk index,TCRI）模型,并进行了计算机仿真.结果表明：水动力模型精度可满足研究与实践要求;基于二分法的LSP模型能快速、可靠收敛;LSP和SCRI/TCRI模型更符合海员通常做法和避碰规则的公认理解.