AbstractElectrification of railway lines provides more economical, faster, safer, and quieter railway transportation as well as significant reductions in carbon emissions. To accomplish the electrification of railway lines, an electrical system needs to be installed on bridges. However, old existing railway bridges were not designed considering a vertical clearance (height) required for electrification. Thus, structural modifications are needed for some steel truss railway bridges. In this paper, a study on structural modifications of a 70-year-old two-span continuous steel truss railway bridge still giving service was presented to increase a safe clearance between the overhead line electrification equipment and rolling stock. Before beginning with modifications, it was firstly aimed to assess the actual bridge condition as well as the load-bearing capacity. For these goals, in situ field dynamic tests were conducted, and a three-dimensional (3D) finite-element (FE) model of the bridge was calibrated based on the field measurements captured. Then, rating factors and safety indices of the bridge were calculated using the calibrated 3D FE model. Finally, a modification procedure including replacement of portal bracing without reducing transversal rigidity and load-carrying capacity of the bridge was proposed.