Browsing by Author "Yerra, Bhanu"

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    The Emergence of Hierarchy in Transportation Networks
    (Springer-Verlag, 2005) Yerra, Bhanu; Levinson, David M
    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 - 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 the 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.
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    Highway Costs and the Efficient Mix of State and Local Funds
    (Transportation Research Board, 2002) Levinson, David M; Yerra, Bhanu
    Transportation networks and governments are both hierarchically organized. In some states most highways are financed by state governments, while in other states similar roads are financed locally. Larger governments attain scale economies. However they also tend to be more bureaucratic and have higher operating costs, all else equal, due to problems such as span of control. This study relates highway expenditure with share of expenditure by state government so that a basis for determining how governments should share expenditure on all roads in a state to attain efficiency in highway costs. For each state three different costs are considered: capital outlay, operations and maintenance, and total costs. Two government layers are considered: state (including federal contributions) and local government. A series of regression models to predict different highway expenditures as a function of utilization, capacity, and funding shares are estimated. We find that there is a share of expenditures by each level of government which results in a minimum expenditure for each funding category (capital, operating). That minimum is not very far from typical state/local mixes found in many states. The results of this study can be applied in formulation of efficient network financing arrangements. Policies can be formulated that can help adjust the financial responsibilities of transportation networks between government layers.
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    How Land Use Shapes the Evolution of Road Networks
    (2006) Levinson, David M; Yerra, Bhanu
    The present research develops an agent-based model to treat the organization, growth, and contraction of network elements. The components model travel demand, revenue, cost, and investment. Revenue earned by links in excess of maintenance costs is invested on the link to until all revenue is consumed. After upgrading (or downgrading) each link in the network, the time period is incremented and the whole process is repeated until an equilibrium is reached or it is clear that it cannot be achieved. The model is tested with three alternative land use patterns: uniform, random, and bell-shaped, to test the effects of land use on resulting network patterns. It is found that similar, but not identical, equilibrium hierarchical networks result in all cases, with the bell-shaped network, with a CBD, having higher level roads concentrated in a belt around the CBD, while the other networks are less concentrated
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    Self Organization of Surface Transportation Networks
    (INFORMS, 2006) Levinson, David M; Yerra, Bhanu
    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 which 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.