Safe transportation of hazardous materials by rail is an important issue in Switzerland. This study analyzes an existing model for the risk of transport of hazardous materials via Swiss railways, in collaboration with the Swiss Federal Office for the Environment. The model is the basis for the risk calculation of hazards for persons for all railway transports of hazardous materials in Switzerland and is published by the Swiss Federal Office of Transport. It includes 155 input variables estimated with different uncertainties. The objective of this study is to determine which input variables possess the strongest influence on the model output (the risk) and should therefore be determined with higher accuracy.
To achieve this objective, different sensitivity analysis methods as suggested by Borgonovo are compared. The risk model is implemented in Maple and the Sobol decomposition is used for a global sensitivity analysis of the input variables. The Sobol method is a variance-based sensitivity analysis that decomposes the variance of the output of the model into contributions due to input variables or sets of input variables. The Sobol indices are calculated analytically by evaluating various integrals in the decomposition. In addition, the stability of the method is investigated by using different ranges of the input variables. As a first cross check, the partial derivatives of all input variables are calculated for the same model. As a second cross check, an independent analysis in Matlab is carried out, based on Monte Carlo simulation of the input variables within their uncertainty range.
The results are stable and consistent among all methods and will be used by the Swiss Federal Office for the Environment to optimize the estimation of the input variables of this risk model.