Integrated models of land use and transportation for the autonomous vehicle revolution

ABSTRACT

The advent of the autonomous vehicle (AV) will affect not only the transportation system, but also future patterns of land development. Integrated land use and transportation models will be critical tools in assessing the path forward with this technology. Key questions with respect to land use impacts of AVs arise from potential changes in sensitivity to travel and reduced demand for parking. It is an open question whether AVs will induce urban sprawl, or whether spatial economies of agglomeration will mitigate any reductions in travel time sensitivity. The deployment of shared fleets of AVs would likely reduce parking demand, producing yet to be explored impacts on property development within existing urban footprints. We perform a critical assessment of currently operational models and their ability to represent the adoption of AVs. We identify the representation of time in such models as a vital component requiring additional development to model this new technology. Existing model applications have focused on the discrete addition of new infrastructure or policy at a fixed point in time, whereas AV adoption will occur incrementally through time. Stated adaptation surveys are recommended as tools to quantify preferences and develop relevant model inputs. It is argued that existing models that assume comparatively static equilibrium have been convenient in the past, but are insufficient to model technology adoption. In contrast, dynamic model frameworks lack sufficient structure to maintain reasonability under large perturbations from base conditions. The ongoing advancement of computing has allowed models to move away from being mechanistic aggregate tools, towards behaviourally rich depictions of individual persons and firms. However, much work remains to move from projections of existing conditions into the future, to the evolution of the spatial economy as it evolves through time in response to new technologies and exogenous stresses. Principles from complex and evolutionary systems theory will be important in the development of models with the capacity to consider such dynamics.     

Development of Green-Naghdi models with a wave-absorbing beach for nonlinear, irregular wave propagation

Two-dimensional and three-dimensional Green-Naghdi (GN) models equipped with a numerical wave-absorbing beach have been developed to simulate nonlinear, regular, and irregular wave propagation. The numerical beach is introduced near the downstream boundary to absorb outgoing waves. An appropriate amount of numerical damping and an appropriate length of numerical beach are investigated using numerical experiments. The results show that the GN models with a numerical beach work very well in simulating wave propagation in water in a small computational domain.     

轨道交通建设与城市道路相结合研究

为有效利用城市土地与空间资源,轨道交通多沿既有或规划城市道路敷设。在项目设计过程中,若未考虑好轨道交通与城市道路的关系,将会引起征地拆迁、道路改造、环境保护等一系列问题,有可能影响项目建设的顺利进行。因此,为提高轨道交通建设质量,从两者的空间关系、线形适应性等方面进行理论分析。结合城市空间规划,从环境适应性、技术可行性与经济合理性等多方面考虑确定合理的空间关系,以技术指标匹配性为参考指标,进行线路走向选择。通过工程实例的对应研究,论证理论分析的合理性及可操作性,可用于指导轨道交通的建设及城市道路的改造。     

超大跨度缆索承重桥梁结构体系

设计和建造跨海连岛大桥是新世纪桥梁工程面临的巨大挑战。超大跨度桥梁并不只是常规概念的外推,需要与之对应的结构体系。从根本上改变缆索承重桥梁的缆索体系,可以突破跨度极限。本文指出了常规结构体系向更大跨度发展的制约因素,从缆索体系的角度介绍了超大跨度斜拉桥、悬索桥以及斜拉 悬索组合桥可能采用的各种体系。这些体系试图在静力、动力方面能远远超出现有限制范围,极大地提高桥梁的跨越能力。同时,新体系的采用也给材料、设计和施工提出了很大的挑战。     

路段动态特征中的交通组成因素研究

基于对交通流建模过程中将车型单一考虑为标准小汽车,忽略了现实交通量中车型的不同构成,本文通过对不同车型的动力特性进行标定,将其特性反映在跟车模型与车道变换模型中,并且利用交通仿真技术,分析了交通量构成对路段行程时间、车速、延误等动态特性指标的影响。     

预应力混凝土箱梁桥横向受力分析方法的研究比较

以洋安大桥主桥5跨预应力混凝土变截面连续箱梁桥为背景,对其横向应力分别采用传统的平面框架法和空间有限元法进行分析比较,结果表明大部分关键截面平面框架法得到的横向应力远大于空间有限元法,在实际设计计算中须谨慎使用平面框架法。     

Influential vectors in fuel consumption by an urban bus operator: Bus route,driver behavior or vehicle type?

Energy costs account for an important share of the total costs of urban and suburban bus operators. The purpose of this paper is to expand empirical research on bus transit operation costs and identify the key factors that influence bus energy efficiency of the overall bus fleet of one operator and aid to the management of its resources.We estimate a set of multivariate regression models, using cross-section dataset of 488 bus drivers operating over 92 days in 2010, in 87 routes with different bus typologies, of a transit company operating in the Lisbon’s Metropolitan Area (LMA), Rodoviária de Lisboa, S.A.Our results confirm the existence of influential variables regarding energy efficiency and these are mainly: vehicle type, commercial speed, road grades over 5% and bus routes; and to a lesser extent driving events such as: sudden longitudinal decelerations and excessive engine rotation. The methodology proved to be useful for the bus operator as a decision-support tool for efficiency optimization purpose at the company level.     

Congestion and pollution consequences of driving-to-school trips: A case study in Beijing

Parents compete for high-quality education for their children by enrolling them in good schools. However, in a Chinese mega-city like Beijing, three factors jointly lead to the spatial separation between schools and homes: the centralized public goods provision mechanism, the historical dependency in school location, and the constrained supply of housing in downtown. Without an adequate number of school buses, this spatial separation of schools and homes triggers the numerous long-distance driving-to-school trips by private vehicle during workday morning rush hours in Beijing. We use the start and end dates of “school holiday” as exogenous repeated shocks to the aggregate traffic congestion, and employ the two-stage least squares (2SLS) regression approach to examine the congestion and pollution consequences of such driving-to-school trips in Beijing. We find that, all else being equal, workdays during school holidays have a traffic congestion index 20% lower than that of non-school-holiday workdays. Such a sharp reduction in congestion leads to a significant decrease in PM₁₀ concentration. Policymakers should lower such “extra” congestion and environmental costs via optimizing the spatial balance between school supply and demand.     

Determination of limiting cavity depths for offshore spudcan foundations in a spatially varying seabed

The importance of accurate prediction of limiting cavity depths during offshore spudcan foundations installation has been variously highlighted in the literature. Nonetheless, most of the previous research is deterministic in nature and confined to homogenous soils. Since offshore clayey soils can be highly spatially variable, there is a practical need to take proper account of the spatial variability in the prediction of limiting cavity depths. In a bid to remedy this situation, large deformation finite element calculations combined with three-dimensional random fields were repeatedly conducted in this study within a Monte-Carlo framework. The continuous penetration of a spudcan initiated from surface was explicitly modeled until a full-localized flow-around mechanism was observed. Spatial variability was found to clearly affect the soil back-flow and thereby the limiting cavity depth, the latter of which takes a range of values that can be approximately modeled as a log-normal distribution. Characteristic limiting cavity depths at various probability levels were ascertained. An algebraic expression was proposed to explicitly predict the characteristic limiting cavity depths in random soils from the fractile. Particular attention was paid to the lower and upper 5% characteristic values, which are likely to be useful for reliability-based design.     

车务可视化信息系统设计与实现

车务可视化信息系统通过三维模型及虚拟漫游的展现形式,将铁路运行及运营的动态信息进行集成和柔性展示,实现旅客服务信息及运输管理相关数据的整合,通过可视化的展现方式既方便旅客及管理人员,又充分展示铁路信息化建设的成果。