Time Gap Modeling under Mixed Traffic Condition: A Statistical Analysis

This paper attempts to model vehicular time gap, which is defined as the time interval between any two successive arrivals of vehicles at a reference point of measurement on a road segment. Such an approach is justified under the non-lane-based heterogeneous traffic conditions prevailing in developing countries such as India, characterized by many “zero” time gaps due to simultaneous arrivals within a given road width. In addition, time gap data are characterized by a significant amount of data in the tail region due to long headways. Nevertheless, many researchers of time gap modeling have used light-tailed distributions that modeled time gaps satisfactorily due to two reasons: (a) The tail data was merged into a single bin; and (b) goodness-of-fit tests such as the Chi-square test, which has many limitations, were used. Further, some researchers have suggested different distributions for the same range of traffic flows, leading to ambiguity in distribution selection. In addition, bin size, which dictates the degree of fit of any distribution, has been ascribed very less importance in time gap modeling. Hence, this paper tries to consolidate and standardize the existing research in time gap modeling research by addressing all these issues. Two new distributions, namely Generalized Pareto (GP) and Generalized Extreme Value (GEV) with better tail modeling properties, have been proposed along with other conventional distribution to model vehicular time gaps over a wide range of flow from 550 vph to 4,100 vph. Two types of goodness-of-fit tests, namely Area-based and Distance-based tests, have been used. It has been found from the study that GP distribution fits the time gap data well (overall and tails) up to a flow range of 1,500 vph based on both kinds of tests, and GEV fits the data well for the flow levels above 1,500 vph based on the area test only.     

Conceptual design of economic hybrid vehicle system using clutchless geared smart transmission

Most hybrid vehicles employ the continuously variable transmission (CVT or eCVT) currently as their choice of the transmissions. Recently, an automated geared transmission (AGT) or dual clutch transmission (DCT) is being tried for some hybrid vehicles for the better fuel economy than the CVT hybrid. However, this AGT or DCT is using automated clutches which require the hydraulic power in addition to the slippage in the clutch plate invoking some energy loss as well as wear. Also, they require a motor with significant power to match to the engine power. The clutchless geared smart transmission (CGST) has no clutch and the clutch function is performed by a planetary gear system controlled by a motor-generator. The hybrid vehicles proposed here using CGST may have some merits in durability, fuel efficiency, and cost since they do not have clutches. The motor used for the clutch function can be also working for power merge with the engine in propelling the vehicle. The proposed hybrid system can be either mild hybrid or full hybrid by adopting a different capacity of battery with much smaller motor-generator due to the planetary gear system compared to the other type hybrid vehicles. In this study, the prospects of newly proposed CGST hybrid system are examined in practical aspects compared with AGT hybrid or DCT hybrid systems.     

An empirical assessment of relational competitive advantage in professional ship management

Intense competition in many sectors across the maritime industry and in professional ship management in particular, means that the quest for achieving competitiveness will continue and intensify. A review of the current strategies across many sectors of the industry indicates the importance of forging stable partnerships for the achievement of competitiveness. Considering that the capability to form a relationship is an intangible resource (as depicted in resource-advantage theory), an empirical assessment in the context of ship management was undertaken. The assessment aimed to identify the type of relationships present in ship management, and succeeded in classifying those relationships into four distinct groups. The central thesis of the paper is that maritime organizations in general, and ship management companies in particular, may utilize their intangible relational resources in order to achieve competitive advantage. Based on the classification of ship management relationships, implications for managers are discussed.     

Impact of Everyday Weather on Individual Daily Travel Behaviours in Perspective: A Literature Review

Despite the hundreds of billions of dollars being spent on infrastructure development -- from roads, rail and airports to energy extraction and power networks to the Internet -- surprisingly little reliable knowledge exists about the performance of these investments in terms of actual costs, benefits and risks. This paper presents results from the first statistically significant study of cost performance in transport infrastructure projects. The sample used is the largest of its kind, covering 258 projects in 20 nations worth approximately US$90 billion (constant 1995 prices). The paper shows with overwhelming statistical significance that in terms of costs transport infrastructure projects do not perform as promised. The conclusion is tested for different project types, different geographical regions and different historical periods. Substantial cost escalation is the rule rather than the exception. For rail, average cost escalation is 45% (SD=38), for fixed links (tunnels and bridges) it is 34% (62) and for roads 20% (30). Cost escalation appears a global phenomenon, existing across 20 nations on five continents. Cost estimates have not improved and cost escalation not decreased over the past 70 years. Cost estimates used in decision-making for transport infrastructure development are highly, systematically and significantly misleading. Large cost escalations combined with large standard deviations translate into large financial risks. However, such risks are typically ignored or underplayed in decision-making, to the detriment of social and economic welfare.     

A Modeling Framework for Bus Rapid Transit Operations Evaluation and Service Planning

Abstract

In this paper, we present a dynamic traffic assignment-simulation modeling framework (DYNASMART-P) to support the evaluation and planning of Bus Rapid Transit (BRT) services in urban transportation networks. The model represents the different characteristics associated with BRT operations such as: exclusive right-of-way lanes, limited-stop service, signal prioritization at congested intersections, and enhanced bus stops to reduce passenger boarding times. A set of simulation experiments is conducted using the model to study the impact of introducing a hypothetical BRT service in the Knoxville area in the State of Tennessee. In these experiments, the different operational characteristics of BRT are evaluated in terms of potential impact on transit ridership and on the interacting auto traffic. The results illustrate the advantages of BRT for increasing transit ridership and improving overall system performance.     

Grain refinement in bearing steels using a double-quenching heat-treatment process

A double-quenching (D/Q) process is proposed for heat-treating high carbon-chromium bearing steels to improve the fatigue properties through refinement of the microstructure. The new heat treatment method has two steps: The first step is a nitrocarburizing process that results in high surface hardness and lowers the transformation temperature. The second step is the same as in the conventional quenching process but can be conducted at a considerably lower temperature than in conventional quenching. The microstructure in the material that is caused by the D/Q heat treatment is much finer than in the conventional Q/T (quenching and tempering) process. In order to quantify the performance of the proposed heat-treatment process, various mechanical property tests are carried out. The rolling contact fatigue life of double-quenched bearing steels was eight times higher than in bearing steels that were treated by conventional Q/T.     

FRP正弦波形夹心桥面板的等效有限元模型

以FRP正弦波形夹心桥面板作为研究对象,得到等效正交各项异性实心板,通过理论分析和数值对比,证明了方法的可行性;采用该法对一实际的FRP正弦波形夹心板桥进行了模态分析。     

青藏线拉萨河特大桥主桥横梁设计

拉萨河特大桥主桥采用 (3 6+ 72 + 10 8+ 72 + 3 6)m五跨三拱连续梁钢管拱组合结构体系。通过对系杆拱桥不同部位横梁受力特点进行分析 ,采取相应的设计措施 ,为系杆拱桥的横梁设计提供一种合理的设计方法。     

隧道检测系统及其在韩国高速铁路隧道的应用

介绍韩国高速铁路隧道安装的健康监测系统,提出基于检测数据诊断隧道衬砌可能破损的新系统识别方法。引入逆算法,即根据已知的形变数据和混凝土衬砌恒载,估计破损的程度和位置。对以刚度均减和裂缝概念为基础建立的两种模型进行效果和优劣比较。对理想化的隧道结构进行数学分析,并用检测数据中常用的白噪声对模型进行适应性研究。结果表明,基于刚度均减方法的模型1对白噪声相对不敏感,而以裂缝概念为基础的模型2由于受刚度减小的影响很小,易于现场应用。