At the railway line north of Amsterdam the substructure of the track has been reconstructed to reduce vibrations at lower frequencies. Such a measure is sought for in the western Holland area where people are annoyed by railway traffic vibrations. Over a length of 300 m a 0.45 m thick concrete slab has been installed directly under the ballast layer. The thickness of the concrete plate has been determined by numerical calculations. To be able to compare the effect of the concrete slap a existing track with heavy passenger train traffic a representative weak soil profile has been chosen for a test site, which was found at the Oosthuizen. At this test site an extensive set of vibration measurements have been conducted to determine the effect of the taken measure and to validate the used numerical procedure to predict the vibrations