One pier and two spans of Malahide Viaduct (Dublin, Ireland) were replaced in 2009 due to bridge scour failure. The new (replaced) parts of the structure are considerable stiffer than the rest of it. An in-service passenger train, instrumented with accelerometers, collected vibration data as it crossed the repaired bridge that serves the Dublin-Belfast railway line. This paper reports on an analysis of the bogie vertical acceleration data. Vibration data collected from 41 train crossings were analysed in the time and frequency domains. Results show that there is (visual) evidence that the stiffened spans vibrate less than the rest of the bridge as the train crosses. Multiple signal responses, grouped by train velocity, add to the evidence of a stiffer section of the bridge where two spans were replaced. Moreover, the observed signals have good spatial repeatability, despite the fact that the effect of load is also acknowledged to have an impact. Overall, the results suggest that instrumented trains can be successfully used for continuous condition monitoring of the railway infrastructure and, consequently, for detecting damage or rehabilitation needs.