The U.S. rail network plays an important role in freight and passenger transportation to meet the market dynamic demands and public needs. Understanding such a network based on the study of its topology provides valuable insights into enhancing its transport efficiency, performance, and resilience. Network topologies can be analyzed as unweighted or weighted networks. Unweighted networks consist of nodes and links that have the same significance, while weighted networks consist of nodes and links with varying network attributes. Such network attributes create distinctions which can be used to assign quantifiable weights to links or nodes; hence, networks with attributes associated to their links or nodes are weighted networks. Accounting for network attributes in topology analysis enhances the understanding of the criticality of nodes and links and provides methods to more objectively maintain and enhance network performance. Examples of network attributes include physical lengths of links, commodity volume transported through links, node significance based on originations and destinations of goods moved, etc. Network attributes can be accounted for in network efficiency analysis. A particular type of network efficiency of interest is associated with the connectedness of its nodes by its links that define its topology, termed in this paper as connectedness efficiency. This proposed indicator can account for network attributes in assessing the topology. Network connectedness efficiency analysis provides insights into the criticality of nodes and links with respect to different network attributes. Such analysis contributes to the enhancement, resilience, and robustness of rail networks, and informs decisions considered by rail managers and executives in planning expansions or route changes or in preparing for possible node or link failures and their potential impacts on network capacity. A case study introducing an aggregated U.S. network along with other fundamental networks is presented to examine different network attributes along with their influence on network connectedness efficiency and impacts of the loss of nodes or links.&nbsp;Some attributes are related to links, such as&nbsp;distance, travel time, and track quality while others are related to nodes, such as location node degree, location significance, and closeness centrality. Using a unified scale for weights is beneficial given that attributes have different measurement units and scales; these attributes’ treatment requires methods to accommodate one or more weight factors for each node or link. Assessing network efficiency is typically based on a single attribute and sometimes concurrently based on more than one attribute. Therefore, methods to normalize weights as a means to unify their scales for aggregation and calculations are needed and presented.&nbsp;Examining network efficiency based on its topology with and without weights offers a basis to assess performance, capability, productivity, resilience, etc. with respect to different attributes in separate or aggregate terms. A network can be efficient with respect to one attribute, but inefficient with respect to another attribute. Quantifiable and objective insights gained into the criticality of links and nodes inform rail planners and managers of their best options for maintaining and improving the overall transport efficiency of their networks.

Connectedness Efficiency for Topological Analysis of Aggregated Railroad Networks: Failure Impacts and Robustness

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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