Exposure-Aware Assessment and Identification of Hazmat-Critical Corridors in the US Freight Railroad Network

Freight railroad corridors that carry hazardous materials (hazmat) are essential to national connectivity, yet disruptions on these corridors can generate disproportionate operational, exposure, and community consequences. This study develops an exposure-aware, two-scale assessment framework for identifying nodes, links, and corridors that are important to system-level resilience and hazmat-related exposure in the US freight railroad network. Two complementary network representations are analyzed for illustration and verification purposes: a high-resolution county-level graph and an aggregate 100-node graph of major gateways and corridors. Shortest paths are computed on distance-weighted links, while exposure is represented separately through population density at nodes and hazmat-related link attributes. The evaluation combines classical centrality measures, exposure-weighted betweenness (EWB), and a disruption-sensitivity diagnostic based on connectedness-efficiency loss under targeted node and link disabilities. Results show strong persistence of major corridor structure across metrics and scales, together with meaningful reordering at the asset level. A Midwest–Plains backbone consistently anchors national connectivity, whereas western mountain gateways and desert crossings emerge as sparse but high-impact bottlenecks because of limited redundancy. At the county scale, finer choke points and branching structures become more visible through the combined effects of topology, exposure, and impact on connectedness efficiency. At the aggregate scale, EWB preserves the principal corridor set while elevating population-critical hubs and hazmat-intensive conduits that are less emphasized by topology-only metrics. Overall, the findings indicate that freight railroad criticality is both scale-sensitive and exposure-dependent. The proposed framework is intended as a system-level assessment to support resilience-oriented planning, including inspection and monitoring prioritization, contingency routing, protective hardening, and rapid-recovery preparation in hazmat-critical freight rail networks.