From Freight Flows to Railroad Bridges: A National Framework for Importance Screening

National freight frameworks consider volume, economic value, and network connectivity, but public data do not directly identify freight dependence at individual railroad bridges. This gap limits consistent national screening for preservation and resilience planning. This study developed a reproducible national workflow to estimate bridge-level freight exposure and identify regional concentrations of important bridges. The workflow assigned Freight Analysis Framework interzonal rail flows to a connected rail network in the contiguous United States, associated eligible bridges with routed edges, and calculated tonnage, value, and distinct origin–destination (OD) reach. These measures formed a zero-preserving, percentile-based rail-bridge freight infrastructure importance index (RB-FII) that gave equal total weight to economic scale and network reach. Tie-inclusive selection and density-based clustering identified important bridge groups, while parallel-track and component-weight sensitivity analyses tested stability. The model routed all 4,911 retained OD pairs, representing 846.80 million short tons and $370.29 billion, and linked 68,326 of 69,356 processed bridges (98.52%) to the routable network. The nominal top 1,000 cutoff yielded 1,003 bridges after retaining ties; 939 formed 32 regional clusters, and 64 remained regionally isolated. Parallel-track alternatives produced bridge-rank correlations of 0.977–0.979 and identical cluster relationships among common bridges. High-emphasis index component weight scenarios retained correlations of 0.988–0.995 with the baseline. The workflow provides an auditable national screening method for directing detailed engineering, operational, and resilience assessments toward bridges and corridors with high modeled freight dependence. The RB-FII is conditional on modeled routes and does not measure observed train routing, bridge condition, failure probability, or disruption loss.