Cost-effectiveness of reductions in greenhouse gas emissions from High-Speed Rail and urban transportation projects in California

A rising trend in state and federal transportation finance is to invest capital dollars into projects which reduce greenhouse gas (GHG) emissions. However, a key metric for comparing projects, the cost-effectiveness of GHG emissions reductions, is highly dependent on the cost-benefit methodology employed in the analysis. Our analysis comparing California High-Speed Rail and three urban transportation projects shows how four different accounting framings bring wide variations in cost per metric tonne of GHG emissions reduced. In our analysis, life-cycle GHG emissions are joined with full cost accounting to better understand the benefits of cap-and-trade investments. Considering only public subsidy for capital, none of the projects appear to be a cost-effective means to reduce GHG emissions (i.e., relative to the current price of GHG emissions in California’s cap-and-trade program at $12.21 per tonne). However, after adjusting for the change in private costs users incur when switching from the counterfactual mode (automobile or aircraft) to the mode enabled by the project, all investments appear to reduce GHG emissions at a net savings to the public. Policy and decision-makers who consider only the capital cost of new transportation projects can be expected to incorrectly assess alternatives and indirect benefits (i.e., how travelers adapt to the new mass transit alternative) should be included in decision-making processes.     

液化天然气(LNG)汽车日常检查方法及维护技术综述

天然气是一种优质的替代燃料,具有污染小、安全系数高、运行费用低等优点。天然气已经成为城市公共交通领域应用最为成功和广泛的车辆替代燃料技术,为推动交通运输行业的节能减排做出了显著的贡献。液化天然气汽车,作为天然气汽车的一种类型,与传统汽柴油车相比,液化天然气汽车安装了包括液化天然气气瓶、气管路及各种控制阀门和仪表在内的专用装置,在对液化天然气汽车进行日常检查时需要针对液化天然气汽车的专用装置进行重点检查。本文则针对液化天然气汽车的特点,对液化天然气汽车的正确使用方法、日常检查方法及维护技术要求、以及相关注意事项三个方面进行了解读,为指导液化天然气汽车进行日常检查与定期维护提供了技术参考。     

天然气车辆推广应用政策措施研究

天然气车辆因其能源结构调整效益和节能减排效益,在道路运输行业应用日趋广泛。但同时,其后期应用过程中的问题也随之显现,为引导道路运输企业更加科学合理的应用天然气汽车,本文通过对当前天然气车辆应用现状的分析,总结应用过程中的问题,对天然气车辆开展成本效益分析,最终提出适合天然气车辆推广应用的政策建议。     

A stochastic model of traffic flow: Theoretical foundations

In a variety of applications of traffic flow, including traffic simulation, real-time estimation and prediction, one requires a probabilistic model of traffic flow. The usual approach to constructing such models involves the addition of random noise terms to deterministic equations, which could lead to negative traffic densities and mean dynamics that are inconsistent with the original deterministic dynamics. This paper offers a new stochastic model of traffic flow that addresses these issues. The source of randomness in the proposed model is the uncertainty inherent in driver gap choice, which is represented by random state dependent vehicle time headways. A wide range of time headway distributions is allowed. From the random time headways, counting processes are defined, which represent cumulative flows across cell boundaries in a discrete space and continuous time conservation framework. We show that our construction implicitly ensures non-negativity of traffic densities and that the fluid limit of the stochastic model is consistent with cell transmission model (CTM) based deterministic dynamics.     

输气管道置换优化研究

置换是输气管道投产试运过程中的重要工艺环节,是复杂的扩散、对流过程。文中介绍了输气管道投产前用氮气置换空气的几种方法,阐述了它们的工作原理与实施步骤,对比分析了它们的优缺点,优选了置换方式,并采用Fluent流体模拟软件建立了输气管道氮气置换数学模型,进行了三维稳态和非稳态数值计算,研究了置换过程中混气段长度随管径、管长、流速变化规律,将理论推导、数值计算和现场数据进行了对比,验证了理论结果的正确性,为现场施工提供了科学依据。     

埋地管道防腐层破损点检测技术综合应用研究

对防腐层完整性检测尤其是对防腐层破损点的精确定位,及对检出大、中面积破损点开挖修补,是确保土壤跟管道的有效绝缘、提高阴极保护效果的关键。文中分析了常用埋地钢质管道防腐层破损点检测技术特点,结合现场检测实践,综合应用多种技术,能有效检测埋地钢质管道防腐层破损点。根据测量数据可以判断破损点大小以及是否开挖修理,在管道安全运行及检测的经济性之间寻找结合点。     

天然气管道干燥方法的对比分析与应用

介绍了天然气管道投产使用的流动气体蒸发法、真空干燥法和干燥剂干燥法的原理和工艺,以及真空干燥和干空气干燥的计算模型。对真空干燥、干空气干燥和二者结合的方法用于管道投产前的干燥进行了研究,提出管道应采用结合干燥法的建议,并对管道干燥所需的时间进行了预测,单独使用真空干燥法比单独使用干空气干燥需时长,且二者结合干燥的方法干燥时间最短。     

国产长输管道焊接施工装备研究

近年来,长输油气管道焊接施工装备技术快速发展,大量新型管道施工装备投入管道工程现场应用,比如管道全位置自动焊机、管道管端坡口机、管道内环缝自动焊机已被分别用于管口焊接、坡口加工、管口组对。在大厚壁、高钢级、大口径管道施工中,这些设备既提高了管道施工效率,也提高了管口的焊接质量。根据实际应用情况,阐述了前述设备的结构、性能和其他技术特点,以使相关技术人员对国产管道施工装备有进一步的认识。     

管道防腐涂层的现状与展望

管道的腐蚀问题是影响管道系统可靠性及使用寿命的关键因素,选择和使用合理的防腐涂层,对管道的安全运行、使用寿命及降低经济成本都具有十分重要的意义。文中简述了管道腐蚀产生的原因,综述了管道防腐涂层的发展概况,着重介绍了液态聚氨酯防腐涂料、无机非金属防腐层、纳米改性材料涂层等管道防腐涂层技术的新发展,提出了这些涂层在管道防腐应用中存在的问题,并对管道防腐涂层的发展前景做了展望。     

管道内防腐层补口技术研究进展

管道内衬或内防腐涂层现场施焊时,焊缝两侧的防腐层会由于高温作用而破坏,使环焊缝处不能得到有效的保护,内补口技术也成为影响管道质量的主要瓶颈。文中介绍了国内外主要的内补口技术,如内补口机法、内衬保护套（管）焊接法、不锈钢接头法、机械连接法等,并指出各方法的特点。文中还就内补口技术的质量控制和研究方向等提出了建议。