Reliable Shortest Path Problems in Stochastic Time-Dependent Networks

This study investigates the time-dependent reliable shortest path problem (TD-RSPP), which is commonly encountered in congested urban road networks. Two variants of TD-RSPP are considered in this study. The first variant is to determine the earliest arrival time and associated reliable shortest path for a given departure time, referred to as the “forward” TD-RSPP. The second problem is to determine the latest departure time and associated reliable shortest path for a given preferred arrival time, referred as the “backward” TD-RSPP. It is shown in this article that TD-RSPP is not reversible. The backward TD-RSPP cannot be solved by the algorithms designed for the forward problem using the reverse search from destination to origin. In this study, two efficient solution algorithms are proposed to solve the forward and backward TD-RSPP exactly and the optimality of proposed algorithms is rigorously proved. The proposed solution algorithms have potential applications in both advanced traveler information systems and stochastic dynamic traffic assignment models.     

Economic appraisal of universal design in transport: Experiences from Norway

Economic assessment of universally designed transport projects has not been studied in depth in the transport planning literature. Universal Design (UD) refers to the design of transport systems in a way that they are accessible to all users, irrespective of the users’ abilities. This definition of UD has not yet gained roots in the transport economic literature. The conventional thinking is that UD is for the few, i.e., the impaired, and given that they are few in numbers, UD projects will generally be unprofitable from a socioeconomic point of view because benefits will be low while investment costs will be too high. The objective of this paper is to prove the opposite: UD projects benefit all users of the facility, whether impaired or not, and the additional costs of implementing them are generally low; hence, their net present values are high and positive. We build on collaborative work between the Norwegian Public Roads Administration (NPRA) and the Institute of Transport Economics (TOI) aimed at creating guidelines for assessing the economic merits of UD projects. Therefore, in this paper, we: (1) define how UD is to be understood in the context of road and public transport; (2) describe the types of benefits and costs that accrue to users if UD projects are implemented; (3) address how the benefits and cost can be valued in monetary terms; and (4) using three different types of projects, demonstrate that UD projects are surprisingly profitable from a socioeconomic point of view. Finally, we address the implications of our findings and explain why governments need to be concerned with UD of transport systems.     

Modeling the day-to-day traffic evolution process after an unexpected network disruption

Although various approaches have been proposed for modeling day-to-day traffic flow evolution, none of them, to the best of our knowledge, have been validated for disrupted networks due to the lack of empirical observations. By carefully studying the driving behavioral changes after the collapse of I-35W Mississippi River Bridge in Minneapolis, Minnesota, we found that most of the existing day-to-day traffic assignment models would not be suitable for modeling the traffic evolution under network disruption, because they assume that drivers’ travel cost perception depends solely on their experiences from previous days. When a significant network change occurs unexpectedly, travelers’ past experience on a traffic network may not be entirely useful because the unexpected network change could disturb the traffic greatly. To remedy this, in this paper, we propose a prediction-correction model to describe the traffic equilibration process. A “predicted” flow pattern is constructed inside the model to accommodate the imperfect perception of congestion that is gradually corrected by actual travel experiences. We also prove rigorously that, under mild assumptions, the proposed prediction-correction process has the user equilibrium flow as a globally attractive point. The proposed model is calibrated and validated with the field data collected after the collapse of I-35W Bridge. This study bridges the gap between theoretical modeling and practical applications of day-to-day traffic equilibration approaches and furthers the understanding of traffic equilibration process after network disruption.     

基于随机模拟的汽车安全带系统约束效能优化

建立了汽车安全带系统的数学模型，并通过试验对模型的有效性进行了验证。基于随机模拟和响应面方法对安全带系统敏感参数的优化，给出了系统约束效能的优化区间，考虑到参数的制造和装配误差，对优化区间内的系统稳健性进行了计算和分析，得到系统约束效能的最优稳定区间。     

CompactPCI热插拔系统设计与应用

热插拔是CPCI系统最重要和最具优势的特点。目前,业界尚没有一种能够同时支持基本热插拔、完全热插拔和高可靠性热插拔的实现方案。提供了一种CPCI热插拔系统,分别从系统架构、软件架构、各组成部分的数据流交互、热插拔驱动以及守护进程的工作流程5个方面阐述了整个系统的硬件和软件实现。该热插拔系统符合CPCI热插拔规范,能够同时支持基本热插拔、完全热插拔和高可靠性热插拔。     

The efficiency of public transport operations – An evaluation using stochastic frontier analysis

The aim of this study is to evaluate the efficiency of public transport operations undertaken in Swedish counties by the Public Transport Authorities (PTA), taking into account the substantial differences in operating conditions between counties. The analysis will be performed using Stochastic Frontier Analysis (SFA) with annual data from 1986 to 2009 for 26 Swedish counties. The analysis shows how the efficiency of the individual counties has changed over time. The results are used to provide a ranking (in terms of efficiency) of the Swedish public transport authorities that can provide a basis for benchmarking. It is concluded that the efficiency of the public transport providers in all counties fell during the observed time period. Defining cost efficiency as the ratio of minimum cost to observed cost, the overall (average) cost efficiency for the industry fell from 85.7% in the eighties to 60.4% for the period from 2000 to 2009. Possible explanations for the development include increased emphasis on route density as well as higher environmental and safety requirements.     

Stochastic Control Model on Rent Seeking

A continuous-time stochastic model is constructed to analyze how to control rent seeking behaviors. Using the stochastic optimization methods based on the modem risky theory, a unique positive solution to the dynamic model is derived. The effects of preference-related parameters on the optimal control level of rent seeking are discussed, and some policy measures are given. The results show that there exists a unique solution to the stochastic dynamic model under some macroeconomic assumptions, and that raising public expenditure may have reverse effects on rent seeking in an underdeveloped or developed economic environment.     

关山特长隧道围岩力学参数取值研究

隧道围岩处于各种结构面环境中,加之取样过程中具有随机性,准确获取围岩力学参数较为困难。应用随机模糊理论,建立隧道围岩参数随机—模糊评价模型,对室内试验数据进行处理,并建立围岩力学参数可信度数学模型,评价参数取值的可靠性,用该方法可以准确地确定围岩力学各个参数,且每个参数都有相当程度的可信度。应用该方法确定了关山特长隧道围岩的弹性模量和变形模量。     

船体梁静水载荷效应统计预报

船体梁静水剪力、弯矩等是由装载状态决定的载荷效应。营运船舶装载记录表明，实际装载状态具有不确定性，由此导致载荷效应发生变异，其统计特性可利用回归公式或随机模拟原理进行估算或预报。通过对油船、散货船、滚装船及集装箱船约2000种随机工况所作的统计分析，表明其静水弯矩等随装载偏差的变化近似于正态分布律，并具有比船体中剖面模数或钢材屈服极限更为显著的变异性。在船舶结构可靠性分析或理性设计中，合理估算并预报这种及异性是必要的。     

Understanding Travel Time Expenditures Around the World: Exploring the Notion of a Travel Time Frontier

Travel behavior researchers have been intrigued by the amount of time that people allocate to travel in a day, i.e., the daily travel time expenditure, commonly referred to as a “travel time budget”. Explorations into the notion of a travel time budget have once again resurfaced in the context of activity-based and time use research in travel behavior modeling. This paper revisits the issue by developing the notion of a travel time frontier (TTF) that is distinct from the actual travel time expenditure or budget of an individual. The TTF is defined in this paper as an intrinsic maximum amount of time that people are willing to allocate for travel. It is treated as an unobserved frontier that influences the actual travel time expenditure measured in travel surveys. Using travel survey datasets from around the world (i.e., US, Switzerland and India), this paper sheds new light on daily travel time expenditures by modeling the unobserved TTF and comparing these frontiers across international contexts. The stochastic frontier modeling methodology is employed to model the unobserved TTF as a production frontier. Separate models are estimated for commuter and non-commuter samples to recognize the differing constraints between these market segments. Comparisons across the international contexts show considerable differences in average unobserved TTF values.