Browsing by Subject "Network growth"
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Item Accessibility: Long-Term Perspectives(Journal of Transport and Land Use, 2008) Axhausen, KayImproved accessibility and its correlate lower generalized cost of contact, travel and transport have been sought by dynamic human societies for their economic and social benefits throughout recorded history. The paper will reflect about this process at a number of different spatial and temporal scales based on a conceptual model. Looking back at European history, it will trace the interaction between Christaller’s logic of local market areas and the idea of (low contact cost) network cities. Focusing on Switzerland since 1950 it will show how network investment changed the relative distribution of population and employment and how this interacted with changes in the preferences of the travelers. Using a recent snapshot of how a substantial sample of Swiss maintain their social networks over often very large areas, it will try to answer the question of what will happen in the future, if the current trend of ever lower costs of contact will persist.Item Beyond Business as Usual: Ensuring the Network We Want Is the Network We Get(2006-09-01) Levinson, David M; de Oca, Norah Montes; Xie, FengThis research, extending the Mn/DOT-funded project If They Come, Will You Build It, assesses the implications of existing trends on future network construction. It compares forecast networks (using models estimated on historical decisions developed with previous research) under alternative budget scenarios (trend, above trend, below trend), with networks constructed according to alternative sets of decision rules developed with Mn/DOT and Metropolitan Council staff. The comparison evaluates alternative futures using a set of performance measures to determine whether the network we would get in the absence of a change in policies (allowing historical policies to go forward) outperforms or underperforms the networks developed by applying suggested decision rules. This evaluation methodology enables new decision rules for network construction (building new links or widening existing links) to be tested. The research suggests a path beyond ?business as usual?.This research incorporates results from the different scenarios tested. It presents the processes, approaches and development to encode historical decision rules. After analyzing flowcharts developed from the interviews of staff at different levels of government, if-then rules are generated for each jurisdiction. This research then describes the details and processes necessary to run the network forecasting models with various decision rules. Results for different scenarios are presented including adding additional constraints for the transportation network expansion and calibration process details. A comparison and analysis between scenarios is made in order to provide a final conclusion on what scenario will produce the greatest benefit for the Twin Cities Metropolitan Area Transportation Network.
Item Cities as Organisms: Allometric Scaling of Urban Road Networks(Journal of Transport and Land Use, 2008) Samaniego, Horacio; Moses, Melanie E.Just as the cardiovascular network distributes energy and materials to cells in an organism, urban road networks distribute energy, materials and people to locations in cities. Understanding the topology of urban networks that connect people and places leads to insights into how cities are organized. This paper proposes a statistical approach to determine features of urban road networks that affect accessibility. Statistics of road networks and traffic patterns across 425 U.S. cities show that urban road networks are much less centralized than biological vascular networks. As a result, per capita road capacity is independent of the spatial extent of cities. In contrast, driving distances depend on the size of the city, although not as much as is predicted by a completely centralized model. This intermediate pattern between centralized and decentralized extremes may reflect a mixture of different travel behaviors. The approach presented here offers a novel macroscopic perspective on the differences between small and large cities and on how road infrastructure and traffic might change as cities grow.Item Does first last? The existence and extent of first mover advantages on spatial networks(Journal of Transport and Land Use, 2011) Levinson, David; Xie, FengThis paper examines the nature of first-mover advantages in the deployment of spatially differentiated surface transport networks. A number of factors explaining the existence of first-mover advantages have been identified in the literature; however, the questions of whether these factors exist in spatial networks, and of how they play out with true capital immobility have remained unanswered. By examining empirical examples of commuter rail and the Underground in London, first-mover advantage is observed and its sources explored. A model of network diffusion is then constructed to replicate the growth of surface transport networks, making it possible to analyze first-mover advantage in a controlled environment. Simulation experiments are conducted, and Spearman rank correlation tests reveal that first-mover advantages can exist in a surface transport network and can become increasingly prominent as the network expands. In addition, the analysis discloses that the extent of first-mover advantages may relate to the initial land use distribution and network redundancy. The sensitivity of simulation results to model parameters are also examined.Item SONIC - System of Network Incremental Connections(2016-07-13) Xie, Feng; Levinson, David M; dlevinson@umn.edu; Levinson, David M; University of Minnesota Nexus Research GroupThe software contains a network-growth simulation model. The logic is based on the strongest-link assumption (ie for a link to be constructed, it must be ranked the highest in terms of increasing accessibility between the two blocks it connects).