A new schedule-based transit assignment model with travel strategies and supply uncertainties

This paper proposes a new scheduled-based transit assignment model. Unlike other schedule-based models in the literature, we consider supply uncertainties and assume that users adopt strategies to travel from their origins to their destinations. We present an analytical formulation to ensure that on-board passengers continuing to the next stop have priority and waiting passengers are loaded on a first-come-first-serve basis. We propose an analytical model that captures the stochastic nature of the transit schedules and in-vehicle travel times due to road conditions, incidents, or adverse weather. We adopt a mean variance approach that can consider the covariance of travel time between links in a space–time graph but still lead to a robust transit network loading procedure when optimal strategies are adopted. The proposed model is formulated as a user equilibrium problem and solved by an MSA-type algorithm. Numerical results are reported to show the effects of supply uncertainties on the travel strategies and departure times of passengers.     

高等级公路养护质量评价体系研究

从公路养护管理的需求出发,将高等级公路作为一类单独的评价对象,依据其使用性能要求,建立了高等级公路养护质量评价流程框架、指标体系,形成了完整的高等级公路养护质量评价体系。针对高等级公路养护质量评价特性,提出了定性、定量相结合的养护质量评价数据采集方法。采用权重模型计算不同层次的养护质量评价指标并在现场评分试验的基础上,采用多元统计理论对模型参数进行回归分析,得出了不同评价模型参数值。     

浅谈鼓式后制动系统防抱死方案的设计

通过鼓式后制动系统数学模型分析，对该系统进行了正向设计及6种不同状态的全过程验算，最终确认后制动器在后减压缩过程中不会再出现自制动或抱死现象。运用该方案，成功对多款量产车型进行了重新设计和整改，取得了很好的市场效益，提高了摩托车行驶安全性和经济效益，并有效缩短了新产品的设计验证周期。     

Competition and disruption in a dynamic urban supply chain

Rapid changes and complexities in business environments have stressed the importance of interactions between partners and competitors, leading supply chains to become the most important element of contemporary business environments. There is a concomitant need for foresight in describing supply chain performance in all operating environments, including those involving punctuated disruptions. Furthermore, the urban metropolis is now widely recognized to be an environment which is especially vulnerable to supply chain disruptions and for which integrated supply chain decisions can produce very substantial net benefits. Accordingly, this paper presents a dynamic supply chain network model formulated as a differential variational inequality; the model is fashioned to allow consideration of supply chain disruption threats to producers, freight carriers, and retail enterprises. The DVI is solved using a fixed-point algorithm, and a simple numerical example, introduced to illustrate how the impacts of supply chain disruptions may be quantified, is presented.     

On the fundamental diagram and supply curves for congested urban networks

Macroscopic fundamental diagrams (MFD) of traffic for some networks have been shown to have similar shape to those for single links. They have erroneously been used to help estimate the level of travel in congested networks. We argue that supply curves, which track vehicles in their passage through congested networks, are needed for this purpose, and that they differ from the performance curves generated from MFD. We use a microsimulation model, DRACULA and two networks, one synthesizing the network for Cambridge, England, and one of the city of York, England, to explore the nature of performance curves and supply curves under differing patterns of demand.We show that supply curves differ from performance curves once the onset of congestion is reached, and that the incorrect use of performance curves to estimate demand can thus seriously underestimate traffic levels, the costs of congestion, and the value of congestion relief measures. We also show that network aggregated supply curves are sensitive to the temporal distribution of demand and, potentially, to the spatial distribution of demand. The shape of the supply curve also differs between origin–destination movements within a given network.We argue that supply curves for higher levels of demand cannot be observed in normal traffic conditions, and specify ways in which they can be determined from microsimulation and, potentially, by extrapolating observed data. We discuss the implications of these findings for conventional modelling of network management policies, and for these policies themselves.     

基于绿色交通理念的深圳市盐田区交通规划探索与实践

绿色交通已经成为建设低碳社会的有效抓手,是当今世界城市交通发展的必然趋势。首先介绍了绿色交通的内涵与基本特征,提出了绿色交通的发展内容与模式;在借鉴国内外绿色交通发展经验的基础上,并在深圳市绿色交通体系及模式的指引下,对深圳市国家生态城区——盐田区进行了绿色交通规划的探索。结合盐田区城市土地空间不足、生态资源受约束的现实条件,采取了空间差异性交通发展模式,并着重分析了地区公共交通系统、自行车、山海步行系统的发展规划思路。     

干线交叉口信号灯线控系统配时设计实例分析

对城市主干道进行"绿波"信号配时设计,可以最大限度地节省车辆停留及等待时间,提高道路设施的综合效益。在交通调查的基础上,对金华市八一南街与李渔路、宾虹路相交的十字交叉口主干道方向进行线控配时方案设计,并利用VISSIM交通模拟软件对线控配时方案进行仿真验证,结果显示通过线控方案设计可以使车辆在交叉口平均延误时间明显减少。     

A competing Markov model for cracking prediction on civil structures

Cracks on the surface of civil structures (e.g. pavement sections, concrete structures) progress in several formations and under different deterioration mechanisms. In monitoring practice, it is often that cracking type with its worst damage level is selected as a representative condition state, while other cracking types and their damage levels are neglected in records, remaining as hidden information. Therefore, the practice in monitoring has a potential to conceal with a bias selection process, which possibly result in not optimal intervention strategies. In overcoming these problems, our paper presents a non-homogeneous Markov hazard model, with competing hazard rates. Cracking condition states are classified in three types (longitudinal crack, horizontal crack, and alligator crack), with three respective damage levels. The dynamic selection of cracking condition states are undergone a competing process of cracking types and damage levels. We apply a numerical solution using Bayesian estimation and Markov Chain Monte Carlo method to solve the problem of high-order integration of complete likelihood function. An empirical study on a data-set of Japanese pavement system is presented to demonstrate the applicability and contribution of the model.     

基于ANP和粗糙集计算权重的绿色铁路客站评估

建设满足"节能环保"要求的绿色铁路客站,是我国铁路发展的趋势所在,因此铁路客站的绿色等级评估是极有必要的。通过建立绿色铁路客站"四节一环保"评价指标体系,以网络层次分析法(ANP)确定指标主观权重,经典粗糙集理论确定指标客观权重,再通过最小相对熵原理对二者进行优化结合,最后用得出的指标综合权重对银川新铁路客站进行绿色星级评估。结果表明:该权重确定方法既克服了因未考虑各指标之间的依存反馈关系而使主观权重不够准确的弊端,又利用相对熵原理优化并减小了主、客观权重结合的偏差,得出科学合理的组合权重,体现本文指标权重确定方法的有效性和优越性,为更加准确地评估铁路客站的绿色等级提供参考。     

高速铁路常用供电方式接地回流研究

分析了在高速铁路常用的供电方式下，即带回流线的直接供电方式和AT供电方式下的接地回流情况，通过对2种供电方式下牵引网的等效电路建模、计算，得到钢轨电流和地中电流分布系数的近似计算公式，并对回流情况进行了分析。