Why new technologies cannot radically improve the quality of urban transportation

In recent years a great deal of time and effort has been expended on the development of new modes of transport for cities. It is argued in this paper that this work is unlikely to be very productive because the major remaining flaw in the provision of transportation services—the inability of one mode to provide a good service to concentrated and dispersed trip ends—seems unavoidable. To make the required breakthrough a new mode must be frugal in its demands for space, flexible in its operation and fast. But an analysis of the performance of existing and prototype modes suggest that there is a fundamental technological barrier that precludes any one mode from performing well in more than two out of these three ways. This implies that any further improvements in travel for the urbanite must be made through existing modes and their derivatives and will be quite limited. It also suggests that the only possible way of substantially improving urban transportation is to build or rebuild towns so that one of the important mode attributes mentioned above is rendered superfluous.     

Transition choice probabilities and welfare analysis in random utility models with imperfect before–after correlation

Welfare in random utility models is used to be analysed on the basis of only the expectation of the compensating variation. De Palma and Kilani (De Palma, A., Kilani, K., 2011. Transition choice probabilities and welfare analysis in additive random utility models. Economic Theory 46(3), 427–454) have developed a framework for conditional welfare analysis which provides analytic expressions of transition choice probabilities and associated welfare measures. The contribution is of practical relevance in transportation because it allows to compute shares of shifters and non-shifters and attribute benefits to them in a rigorous way. In De Palma and Kilani (2011) the usual assumption of unchanged random terms before and after is made.The paper generalises the framework for conditional welfare analysis to cases of imperfect before–after association of the random terms. The joint before–after distribution of the random terms is introduced with postulated properties in terms of marginal distributions and covariance matrix. Analytic expressions, based on the probability density function and the cumulative distribution function of the joint before–after distribution, and simulation procedures for computation of the transition choice probabilities and the conditional expectations of the compensating variation are provided. Results are specialised for multinomial logit and probit. In the case without income effects, it is proved that the unconditional expectation of the compensating variation depends only on the marginal distributions.The theory is illustrated by a numerical example which refers to a multinomial logit applied to the choice of the transport mode with two specifications, one without and one with income effects. Results show that transition probabilities and conditional welfare measures are affected significantly by the assumption on the before–after correlation. The variability in the transition probabilities across transitions tends to decrease as the before–after correlation decreases. In the extreme case of independent random terms, the conditional expectations of the compensating variation tend to be close to the unconditional expectation.     

CTCS-2级列控区段车站站场改造过渡方案

结合工程实际提出了CTCS-2级列控区段车站在站场改造工程中列控系统过渡的2种方案:一种是在CTCS-2级方式下过渡,另一种是在CTCS-0级方式下过渡,论述了两种方案的实施条件及实现方法。     

宁高城际轨道交通线路技术标准研究

宁高城际高淳段作为江苏沿江城市群轨道交通网中的一条重要线路,联系了南京市主城区、东山副城、溧水区石湫镇和高淳区,承担南京市主城区与高淳区间的远距离轨道交通。前期系统制式专题研究确定,本线的速度目标值为120km/h,车辆选用B型车4辆编组。但我国尚无与之相应的轨道交通线路设计规范,因此实际设计中需要参照地铁或国铁相关规范。而本线线路的平、纵面设计参数与地铁和国铁均有较大差异,不能完全参考《地铁设计规范》或《铁路线路设计规范》,因此必须对本线的关键技术参数进行专题研究,根据本线的功能定位和特点选取合适的技术标准,计算出关键技术参数应用于工程设计。     

T型驳船过渡区域设计及强度分析

T型驳船可以显著提升驳船的最大导管架下水能力和最大组块浮托安装能力,在其船中为船宽过渡区,同时最大弯矩和剪力也出现在该区域,导致其结构复杂。目前已经建成的T型驳船均为方驳改造而成。通过对一艘新建T型驳船过渡区域的结构进行合理设计,同时完成不同设计工况的有限元强度分析,使结构更加可靠,减少了以往改造驳船造成的复杂结构和应力集中现象,同时满足规范及使用要求。     

双块式无砟-有砟轨道过渡段不平顺及动响应分析

通过对现场双块式无砟轨道-有砟轨道过渡段的调研发现过渡段存在有砟轨道轨枕空吊、辅助轨缺失、辅助轨扣件缺失等现象,针对这些现象结合综合检测列车轨道几何数据对过渡段的轨道几何演变规律进行分析,同时运用仿真计算的方法对过渡段在不同不平顺和不同运营速度条件下的动响应进行计算。经研究,无砟轨道和有砟轨道过渡位置易产生幅值相对较大的高低不平顺,随着时间的增加高低不平顺易逐渐恶化。经分析,辅助轨可提高一定的轨道刚度,削减部分来自轨枕空吊对行车产生的不利影响和行车过程中轨道的动态不平顺,并且过渡段对250 km/h以下的运营速度具有一定的适应性,而对300~350 km/h的速度仅在不平顺状况良好的情况下表现出适应性。     

沪昆高铁引入武广高铁长沙南站武广场信号过渡设计及开通方案研究

以杭长高速铁路引入武广高速铁路长沙南站武广场过渡设计为例,详细介绍运营中的高速铁路车站信号系统过渡设计方案,总结各种类型插入道岔的过渡方法、插入道岔的联锁试验方法、信号系统(联锁、列控、CTC、临时限速、RBC、微机监测)的模拟演练方法。     

船舶下水横移架加固后的性能测试与分析

用电测法对加固后的船舶下水横移架结构进行了测试和分析,为提高春承载能力提供了科学依据。     

浅析桥头跳车的成因与防治

从分析桥头跳车的成因出发,对有代表性的几种防治方法进行粗浅的探讨。     

粉体喷射搅拌桩处理软土地基施工技术

粉体喷射搅拌桩处理软土地基技术是加固软土地基的一种新方法,应用于软基段的高路堤、桥梁、结构物的基础和两侧,经加固处理后的粉喷桩主体与周围地基共同作用构成复合地基,提高了地基承载能力,增加了路基和结构物的稳定性。对粉喷桩所用设备的性能、施工工艺、结构物的布桩形式、质量保证措施、施工组织、现场施工记录及检测项目、质量标准均作了较详细的介绍。