Measuring Robustness and Coverage of Transportation Networks with Multiple Routes and Hubs

Robustness, or the resilience of a system to failures and attacks without changing its mode of operation, is an increasingly important characteristic of networks. Even though there are several measures of network robustness, they are not applicable to networks with several links between the same pair of nodes (multiline networks), such as transportation systems. A local index and a set of global indexes are introduced to capture the robustness of having multiple connections between the same nodes. These new indexes are designed to uncover the potential vulnerabilities of network components (i.e., hubs, terminals, and lines) to possible malfunctions that might not be well identified with traditional connectivity matrix–based methods. Results of these measures are compared with traditional network connectivity and robustness indexes for both simulated networks that vary topologically and are each composed of multiple lines that overlap in connectivity and a set of representative rail systems in the United States. A discussion of the applicability of these new multiline robustness measures for decision makers and transportation planners to prioritize the development, protection, or maintenance of network components is provided.