The carbon impact of transportation is large and requires sustainable solutions. With expected population growth, rail transportation plays a vital role in facilitating a greener Europe. The expansion of the rail infrastructure is therefore of essential importance for future challenges. One key aspect to consider is the impact of track irregularities, which are imperfections in track geometry. These irregularities have a significant dynamic impact on bridge responses during train passage and are addressed in the regulations through a dynamic amplification factor (DAF) 𝜑′′. The design value of the DAF, suggested in the regulations, is based on simplified models during the 1970s. Previous studies have indicated an overestimation of the DAF and suggested lower DAF than the current regulations. However, these studies were conducted using synthetic mathematical generators for track irregularities. Consequently, there is now a growing interest in evaluating the factor based on real measurements of these irregularities. In general, decreasing DAF values could potentially enhance the capacity of existing bridges.This study aims to extend previous findings by investigating the impact of track irregularity amplitudes on the dynamic response of bridges, even when using real measurements to record these irregularities. It seeks to determine whether the standard deviation of the variation in the track geometry directly affects the bridge's dynamic responses. Additionally, the study aims to explore the correlation between dynamic bridge responses when track irregularities are generated from measurements versus using a Power Spectral Density (PSD) function. This investigation will provide insights into the accuracy of using PSD functions to model track irregularities in train-track-bridge interaction (TTBI) systems. Furthermore, the study aims to assess whether the dynamic amplification factor accounting for track irregularities is overly conservative in the design codes for short bridges. Previous research concluded a significant overestimation of the factor, and the study aims to verify if similar conclusions can be drawn using real measured deviations of track geometry. Ultimately, the study contributes to the development of more precise design for short railway bridges, and better considering the effects of track irregularities in TTBI systems.The thesis findings showed a direct impact between the amplitude or the standard deviation of the measured track irregularities and the DAF of the bridge responses. As the amplitude of track irregularities increases or decreases, the standard deviation changes proportionally, thereby affecting the DAF in a nearly direct proportion. Although slight variations in the ratio occur within a range of up to 20%, it was concluded that the relationship between the standard deviation of track irregularities and the DAF is mainly characterized as proportional.Another conclusion drawn from this study is that the standard deviation of the track irregularities above the bridge span plays an essential role in exciting the bridge responses and serves as highly reliable approach for an appropriate value to be set into the German PSD function. Implementing this representative standard deviation in the PSD function yields bridge responses that closely align with the outcome of measured track irregularities.Finally, it is ascertained that the design values of the DAF 𝜑′′ according to the Eurocode reveal a substantial overestimation by a minimum of 100% in comparison to the model result of the 95th percentiles of the DAF with respect to the deflection, shear force and bending moment of the short to medium-span bridges when utilizing measured track irregularities from the Malmbanan line. Nevertheless, there remains a possibility for its validity in cases where high deviations in the track geometry above the bridges. In Sweden and many other countries, half the value of the DAF according to the Eurocode could be utilized, i.e., 𝜑′′/2. The implementation of adopting half of the Eurocode's DAF value is deemed reasonable based on the finding of this study.