Sensitivity of Input Parameter on CNOSSOS-EU Railway Emission Levels

Abstract

The United Kingdom Department for Food and Rural Affairs (Defra) commissioned a series of studies investigating the sensitivity of the CNOSSOS-EU noise assessment method. CNOSSOS-EU presents challenges in terms of input data accuracy and availability. For this reason, the studies were commissioned to support data decision making and quantify potential uncertainty in Defra's national noise model. The quality framework set out in Directive 996/2014 requires uncertainty in rail emission levels at source to correspond to an uncertainty of ±2dB(A). Due to the CNOSSOS-EU rail emission model being of multivariate complexity, and the multitude of possible parameter combinations, a scenario and parametric-based approach was taken to the study. The variation in rail emission levels was presented for each parameter for a set of rail vehicle speeds and rail infrastructure scenarios. The results of the analysis indicated which input parameters the CNOSSOS-EU rail noise emission model is most sensitive to. It was found that emissions are most sensitive to changes in the number of axles on the vehicle (i.e. wheel / rail interaction), the density of track joints (impact noise), the curvature of the track (squeal noise), and the construction of bridges (structural resonances). However, the choice of rail roughness, vehicle transfer function, and track transfer function (except in the case of direct fastenings) were found to have a limited impact on rail emission levels.