On the Importance of Accuracy of Geographic Model Data for Noise Impact Studies

Since 1 July 2012, ProRail has to work with a new legal system of noise production ceilings (NPCs) to control the noise impact of the railway traffic on its network. The new system requires that ProRail computes the noise impact of the yearly traffic on about 60 000 reference points. In addition, ProRail has to demonstrate that the noise does not exceed the NPC at any point. ProRail has to compute the noise level at each reference point using the Dutch computation method SRMII (which is the recommended European interim computation method for railway noise). This model has to be updated yearly to reflect all changes in the network and surroundings. The data for the model comes from different sources. It is possible that small changes in the model are introduced by small inaccuracies in the data collection process. A source of small changes is the collection of geographic data with photogrammetric measurements with its inherent measurement and processing (in) accuracy. To investigate the sensitivity of the calculations to small data collection inaccuracies, we have done an extensive parameter study. We performed parameter variations in the national-scale model and analyzed the resulting change in noise level on a statistical basis. This paper presents the results of this study and shows that the accuracy of the height information is crucial.