This paper discusses the ways and means by which Irish Rail has been dealing over the years with aging bridge structures, aiming to improve their performance and resilience in a sustainable manner. The paper outlines the methods for refining the assessments of the structural capacity of historic bridges by the application of site-specific loading and modern computational dynamic analysis to evaluate the performance existing railway bridges. The important phenomena, such us dynamic amplification, serviceability-critical bridge and train accelerations, as well as bridge-train interaction and resonance are outlined. Irish Rail’s methods of improving the performance of these bridges are discussed, with the particular focus on the sustainable methods of strengthening and improving the resilience of historic railway bridges.