转向梯形驱动机构的运动分析及优化设计

转向梯形驱动机构的空间布置对汽车的操纵稳定性影响很大。本文以常见的非独立悬架结构为例,建立空间几何模型进行运动分析,提出同时满足"与前悬架运动协调"和"左右转向力均匀"两方面要求的转向梯形驱动机构优化设计方法。实践应用表明该方法可行。     

轮胎非稳态侧偏特性在空间域内的仿真研究

本文根据胎体复杂变形的轮胎非稳态侧偏特性理论模型在空间域内的表达式,推导出侧向力和回正力矩关于转动角与侧向位移的积分表达式,将其离散化并实现了非稳态侧偏特性在空间域内的仿真,最后给出了轮胎在几种典型输入时的仿真结果。     

Macroscopic Fundamental Diagrams: A cross-comparison of estimation methods

This paper aims to cross-compare existing estimation methods for the Macroscopic Fundamental Diagram. Raw data are provided by a mesoscopic simulation tool for two typical networks that mimic an urban corridor and a meshed urban center. We mainly focus on homogenous network loading in order to fairly cross-compare the different methods with the analytical reference. It appears that the only way to estimate the MFD without bias is to have the full information of vehicle trajectories over the network and to apply Edie’s definitions. Combining information from probes (mean network speed) and loop detectors (mean network flow) also provides accurate results even for low sampling rate (<10%). Loop detectors fail to provide a good estimation for mean network speed or density because they cannot capture the traffic spatial dynamics over links. This paper proposes a simple adjustment technic in order to reduce the discrepancy when only loop detectors are available.     

Assessing social equity in distance based transit fares using a model of travel behavior

The goal of this study is to develop and apply a new method for assessing social equity impacts of distance-based public transit fares. Shifting to a distance-based fare structure can disproportionately favor or penalize different subgroups of a population based on variations in settlement patterns, travel needs, and most importantly, transit use. According to federal law, such disparities must be evaluated by the transit agency, but the area-based techniques identified by the Federal Transit Authority for assessing discrimination fail to account for disparities in distances travelled by transit users. This means that transit agencies currently lack guidelines for assessing the social equity impacts of replacing flat fare with distance-based fare structures. Our solution is to incorporate a joint ordinal/continuous model of trip generation and distance travelled into a GIS Decision Support System. The system enables a transit planner to visualize and compare distance travelled and transit-cost maps for different population profiles and fare structures. We apply the method to a case study in the Wasatch Front, Utah, where the Utah Transit Authority is exploring a switch to a distance-based fare structure. The analysis reveals that overall distance-based fares benefit low-income, elderly, and non-white populations. However, the effect is geographically uneven, and may be negative for members of these groups living on the urban fringe.     

A latent variable representation of count data models to accommodate spatial and temporal dependence: Application to predicting crash frequency at intersections

This paper proposes a reformulation of count models as a special case of generalized ordered-response models in which a single latent continuous variable is partitioned into mutually exclusive intervals. Using this equivalent latent variable-based generalized ordered response framework for count data models, we are then able to gainfully and efficiently introduce temporal and spatial dependencies through the latent continuous variables. Our formulation also allows handling excess zeros in correlated count data, a phenomenon that is commonly found in practice. A composite marginal likelihood inference approach is used to estimate model parameters. The modeling framework is applied to predict crash frequency at urban intersections in Arlington, Texas. The sample is drawn from the Texas Department of Transportation (TxDOT) crash incident files between 2003 and 2009, resulting in 1190 intersection-year observations. The results reveal the presence of intersection-specific time-invariant unobserved components influencing crash propensity and a spatial lag structure to characterize spatial dependence. Roadway configuration, approach roadway functional types, traffic control type, total daily entering traffic volumes and the split of volumes between approaches are all important variables in determining crash frequency at intersections.     

On accommodating spatial dependence in bicycle and pedestrian injury counts by severity level

This paper proposes a new spatial multivariate count model to jointly analyze the traffic crash-related counts of pedestrians and bicyclists by injury severity. The modeling framework is applied to predict injury counts at a Census tract level, based on crash data from Manhattan, New York. The results highlight the need to use a multivariate modeling system for the analysis of injury counts by road-user type and injury severity level, while also accommodating spatial dependence effects in injury counts.     

Use of ecological footprinting to explore alternative transport policy scenarios in an Irish city-region

The objective of this paper is to compare the ecological footprint for travel-commuting patterns for the residents of an Irish city-region, that is Limerick city-region, in 1996 and 2002. Scenario building, based on ecological footprint analysis, is used to estimate the impact of different policy choices for 2010. The optimal policy mix for sustainable travel is proposed and consists of a mix of reduced demand through travel demand measures, better spatial planning and technological improvements in fuel economy.     

BIM技术在铁路信号工程设计中的应用研究

铁路信号工程具有多子系统、设备离散布置、系统网络连接、信号集中控制、表达抽象及逻辑制约关系复杂等特点。围绕基于BIM技术实现多源异构系统之间的信息交换这一核心目的,分析当前铁路信号工程领域BIM相关技术标准及建设现状,从铁路信号工程设计的信息交换维度出发,探讨信号专业参与协同平台研发的必要性和需要解决的实际问题,提出信息化辅助设计方案,并通过二维可视化辅助设计软件进行验证。研究表明:对于铁路信号工程设计的BIM应用,不能照搬现有的技术,需要结合本专业的设计特点,以信息交换为核心进行相应的辅助设计软件开发,提升铁路信号工程设计的信息化水平和设计效率。     

Incumbent responses to low-cost airline entry and exit: A spatial autoregressive panel data analysis

While the US airline industry has been substantially transformed in recent years by the growth of low-cost airlines, the cost-saving benefits of lower airfares are difficult to gauge empirically. There are two important ways in which this paper contributes to the existing literature on the impact of the low-cost carriers (LCCs). First, the availability of route-level panel data allows us to examine the role of the LCCs in the long-run adjustment of airfares as well as the responses of the incumbent carriers to LCC entry and exit in a dynamic setting. Second, we capitalize on recent developments in spatial econometrics and explicitly model the spatial dependence among adjacent airline routes, an issue often ignored by previous studies. Although most of the pro-competitive effects of LCC entry take place after entry, we find evidence that the incumbent carriers also cut airfares in anticipation of entry by the LCCs. Moreover fares remain lower even after Southwest Airlines exits. Our empirical analysis confirms the spatial dependence among airfares in adjacent routes, provides estimates of the consumer benefits from lower airfares in routes affected by LCCs, and shows that there are substantial indirect benefits, i.e. lower fares in spatially-linked, nearby routes.