The Experts below are selected from a list of 36615 Experts worldwide ranked by ideXlab platform
Anna Nagurney - One of the best experts on this subject based on the ideXlab platform.
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Sustainable Transportation Networks
2020Co-Authors: Anna NagurneyAbstract:Transportation Networks are essential to the functioning of societies and economies and provide the infrastructure for the movement of people and goods over space and time. The existence and utilization of Transportation Networks are fundamental to the modern age and the negative effects of congestion and pollution associated with their increasing usage demand urgent attention.
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the negation of the braess paradox as demand increases the wisdom of crowds in Transportation Networks
EPL, 2010Co-Authors: Anna NagurneyAbstract:In the well-known Braess paradox (Braess D., Unternehmenforschung, 12 (1968) 258), the addition of a new route in a specific congested Transportation network made all the travelers worse off in terms of their individual travel cost (time). In this paper, we consider the hypothesis that, in congested Networks, the Braess paradox may "disappear" under higher demands, and we prove this hypothesis by deriving a formula that provides the increase in demand that will guarantee that the addition of that new route will no longer increase travel cost since the new path will no longer be used. This result is established for any network in which the Braess paradox originally occurs. This suggests that, in the case of congested, noncooperative Networks, of which Transportation Networks are a prime example, a higher demand will negate the counterintuitive phenomenon known as the Braess paradox. At the same time, this result demonstrates that extreme caution should be taken in the design of network infrastructure, including Transportation Networks, since at higher demands, new routes/pathways may not even be used!
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sustainable supply chain and Transportation Networks
International Journal of Sustainable Transportation, 2007Co-Authors: Anna Nagurney, Trisha WoolleyAbstract:ABSTRACT In this paper, we show how sustainable supply chains can be transformed into and studied as Transportation Networks. Specifically, we develop a new supply chain model in which the manufacturers can produce the homogeneous product in different manufacturing plants with associated distinct environmental emissions. We assume that the manufacturers, the retailers with which they transact, as well as the consumers at the demand markets for the product are multicriteria decision-makers with the environmental criteria weighted distinctly by the different decision-makers. We derive the optimality conditions and the equilibrium conditions, which are then shown to satisfy a variational inequality problem. We prove that the supply chain model with environmental concerns can be reformulated and solved as an elastic demand Transportation network equilibrium problem. Numerical supply chain examples are presented for illustration purposes. This paper, hence, begins the construction of a bridge between sustainab...
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congested urban Transportation Networks and emission paradoxes
Transportation Research Part D-transport and Environment, 2000Co-Authors: Anna NagurneyAbstract:Abstract In this paper, we identify three distinct paradoxical phenomena that can occur in congested urban Transportation Networks as regards the total emissions generated, which demonstrate that so-called `improvements' to the Transportation network may result in increases in total emissions generated. In particular, we illustrate, through specific examples, the following: (1) the addition of a road may result in an increase in total emissions with no change in travel demand, (2) the total emissions may increase with a decrease in travel demand and (3) the improvement of a road in terms of travel cost may result in an increase in total emissions without a change in the travel demand. These examples demonstrate that the network topology, cost structure, as well as the travel demand structure must be taken into consideration in any policy system aimed towards the reduction of emissions due to motor vehicles.
David M Levinson - One of the best experts on this subject based on the ideXlab platform.
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modeling the growth of Transportation Networks a comprehensive review
Networks and Spatial Economics, 2009Co-Authors: David M LevinsonAbstract:This paper reviews the progress that has been made over the last half-century in modeling and analyzing the growth of Transportation Networks. An overview of studies has been provided following five main streams: network growth in transport geography; traffic flow, Transportation planning, and network growth; statistical analyses of network growth; economics of network growth; and network science. In recognition of the vast advances through decades in terms of exploring underlying growth mechanisms and developing effective network growth models, the authors also point out the challenges that are faced to model the complex process of transport development.
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topological evolution of surface Transportation Networks
Computers Environment and Urban Systems, 2009Co-Authors: David M LevinsonAbstract:This study explores the topological evolution of surface Transportation Networks, using empirical evidence and a simulation model validated on that data. Evolution is an iterative process of interaction, investment, and disinvestment. The temporal change of topological attributes for the network is also evaluated using measures of connectivity, density, heterogeneity, and connection patterns. The simulation model is validated using historical data from the Indiana interurban network. Statistical analyses suggest that the simulation model performs well in predicting the sequence of link abandonment in the interurban network as well as the temporal change of topological attributes. The simulation model is then applied on different idealized network structures. Typical connection patterns such as rings, webs, hub-and-spokes, and cul-de-sac emerge in the Networks; the spontaneous organization of network hierarchies, the temporal change of spacing between parallel links, and the rise-and-fall of places in terms of their relative importance are also observed, providing evidence for the claim that network topology is an emergent property of network dynamics.
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self organization of surface Transportation Networks
Transportation Science, 2006Co-Authors: David M Levinson, Bhanu YerraAbstract:This research investigates the self-organization of surface Transportation Networks. Using a travel demand model coupled with revenue, cost, and investment models, experiments are run under a variety of parameters on a grid network. It is found that roads, contiguous sections of multiple links operating with similar characteristics, and hierarchies of roads emerge under a broad range of assumptions from Networks with neither defined roads nor clearly organized hierarchies. The factors that drive this are the (dis)economies of scale, the presence of boundaries, and any initial asymmetry in the network. This research thus finds that roads and hierarchies, which are often thought to be the product of conscious design, can also arise without such intention.
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the emergence of hierarchy in Transportation Networks
Annals of Regional Science, 2005Co-Authors: Bhanu Yerra, David M LevinsonAbstract:A Transportation network is a complex system that exhibits the properties of self-organization and emergence. Previous research in dynamics related to Transportation Networks focuses on traffic assignment or traffic management. This research concentrates on the dynamics of the orientation of major roads in a network and abstractly models these dynamics to understand the basic properties of Transportation Networks. A model is developed to capture the dynamics that leads to a hierarchical arrangement of roads for a given network structure and land use distribution. Localized investment rules, wherein revenue produced by traffic on a link is invested for that link's own development, are employed. Under reasonable parameters, these investment rules, coupled with traveler behavior, and underlying network topology result in the emergence of a hierarchical pattern. Hypothetical Networks subject to certain conditions are tested with this model to explore their network properties. Though hierarchies seem to be designed by planners and engineers, the results show that they are intrinsic properties of Networks. Also, the results show that roads, specific routes with continuous attributes, are emergent properties of Transportation Networks.
Andrew P Tarko - One of the best experts on this subject based on the ideXlab platform.
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calibration of safety prediction models for planning Transportation Networks
Transportation Research Record, 2006Co-Authors: Andrew P TarkoAbstract:The current planning practice addresses safety implicitly as a by-product of adding capacity and operational efficiency to the Transportation system. Safety-conscious planning is a new proactive approach to the prevention of crashes based on establishing inherently safe Transportation Networks through integrating consideration of safety into the Transportation planning process. One of the major concerns in predicting crashes in Transportation Networks is the applicability and accuracy of crash prediction models. The paper presents two alternative formulations of the calibration problem consistent with the maximum likelihood approach. The proposed formulations can be viewed as a generalized version of the existing calibration procedure proposed in the past for individual crash prediction models. The formulations are useful for road Networks and for any Transportation mode, provided that the needed prediction models are available. The proposed calibration applied to individual elements of the test network y...
Trisha Woolley - One of the best experts on this subject based on the ideXlab platform.
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sustainable supply chain and Transportation Networks
International Journal of Sustainable Transportation, 2007Co-Authors: Anna Nagurney, Trisha WoolleyAbstract:ABSTRACT In this paper, we show how sustainable supply chains can be transformed into and studied as Transportation Networks. Specifically, we develop a new supply chain model in which the manufacturers can produce the homogeneous product in different manufacturing plants with associated distinct environmental emissions. We assume that the manufacturers, the retailers with which they transact, as well as the consumers at the demand markets for the product are multicriteria decision-makers with the environmental criteria weighted distinctly by the different decision-makers. We derive the optimality conditions and the equilibrium conditions, which are then shown to satisfy a variational inequality problem. We prove that the supply chain model with environmental concerns can be reformulated and solved as an elastic demand Transportation network equilibrium problem. Numerical supply chain examples are presented for illustration purposes. This paper, hence, begins the construction of a bridge between sustainab...
Nikolas Geroliminis - One of the best experts on this subject based on the ideXlab platform.
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on the spatial partitioning of urban Transportation Networks
Transportation Research Part B-methodological, 2012Co-Authors: Yuxuan Ji, Nikolas GeroliminisAbstract:It has been recently shown that a macroscopic fundamental diagram (MFD) linking space-mean network flow, density and speed exists in the urban Transportation Networks under some conditions. An MFD is further well defined if the network is homogeneous with links of similar properties. This collective behavior concept can also be utilized to introduce simple control strategies to improve mobility in homogeneous city centers without the need for details in individual links. However many real urban Transportation Networks are heterogeneous with different levels of congestion. In order to study the existence of MFD and the feasibility of simple control strategies to improve network performance in heterogeneously congested Networks, this paper focuses on the clustering of Transportation Networks based on the spatial features of congestion during a specific time period. Insights are provided on how to extend this framework in the dynamic case. The objectives of partitioning are to obtain (i) small variance of link densities within a cluster which increases the network flow for the same average density and (ii) spatial compactness of each cluster which makes feasible the application of perimeter control strategies. Therefore, a partitioning mechanism which consists of three consecutive algorithms, is designed to minimize the variance of link densities while maintaining the spatial compactness of the clusters. Firstly, an over segmenting of the network is provided by a sophisticated algorithm (Normalized Cut). Secondly, a merging algorithm is developed based on initial segmenting and a rough partitioning of the network is obtained. Finally, a boundary adjustment algorithm is designed to further improve the quality of partitioning by decreasing the variance of link densities while keeping the spatial compactness of the clusters. In addition, both density variance and shape smoothness metrics are introduced to identify the desired number of clusters and evaluate the partitioning results. These results show that both the objectives of small variance and spatial compactness can be achieved with this partitioning mechanism. A simulation in a real urban Transportation network further demonstrates the superiority of the proposed method in effectiveness and robustness compared with other clustering algorithms.
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Exploring spatial characteristics of urban Transportation Networks
2011 14th International IEEE Conference on Intelligent Transportation Systems (ITSC), 2011Co-Authors: Yuxuan Ji, Nikolas GeroliminisAbstract:It has been shown recently that a Macroscopic Fundamental Diagram (MFD) exists in urban Transportation Networks under certain conditions. However, MFD is not universally expected. Previous research demonstrates the existence of MFDs in homogeneous Networks with similar link densities. More recent work focuses on the partitioning of a heterogeneous Transportation network based on different congestion levels. A desired partitioning produces homogeneous regions with similar link densities to guarantee a well-defined MFD and spatially compact shapes to ease the implementation of control measurements [1]. Based on recently proposed partitioning mechanism, this paper further explores the spatial characteristics of sub-Networks (sub-regions or clusters) in urban Transportation Networks. In this paper, a metric is defined to evaluate the spatial compactness of each cluster in the network. In order to obtain the metric, a fast graph traversal algorithm is proposed, which can produce a clockwise sequence for the spatially coordinated boundary nodes along a network. The algorithm takes O(n) and the effectiveness is proved and validated. By applying the boundary smoothness metric to our previous clustering results, we show that the spatial compactness is appropriately guaranteed for each region and the future control policies can therefore be easily implemented based on the partitioning and MFDs. The proposed algorithms can have more general applications in fields of network and graph theory.
