Acoustic specialists have developed a computer model which allows to calculate noise levels along the entire Swiss rail network. The program describes how much sound is radiated and how it is attenuated. The results will one day show in high precision where residents are particularly exposed to noise and what abatement measures will be most effective in protecting them.Goods trains move at night because during daytime the Swiss rail system is used to full capacity by passenger traffic. Unfortunately, it is goods trains which make the most noise – and they operate at exactly the time when most people want to sleep. If the policy of shifting goods transport from the roads to the rail network is to succeed, then goods trains must be made significantly quieter.
The Swiss Federal Office for the Environment (FOEN) therefore tasked a team of scientists of Empa’s with the development of a computer model to simulate noise levels along the Swiss rail network. sonRAIL, the name given to the model, was intended to provide not just noise maps but to calculate the sound exposure of individual buildings. The model thus identifies what remedial measures would be most effective. Federal and local authorities can therefore use sonRAIL to calculate sound levels around existing and planned railway lines and to evaluate the effectiveness of their countermeasures. A noise barrier reduces the rolling noise of the wheels, it is true, but does not protect against the drone of the ventilation system on the roof of a wagon. It is important, therefore, that the researchers do not just focus on wheel-rail noise, but view the problem as a whole, regarding the train as a complete system.
Measuring the noise from 15,000 trains
The acoustic expert Jean Marc Wunderli, together with an international team of scientists involved with the development of sonRAIL, have collected an enormous quantity of data. Between 2007 and 2009 they made measurements of some 15,000 train passings at eighteen locations. In doing so they identified sound sources at various heights along the train, allowing them, together with project partners from the Technical University of Berlin, to describe in detail the noise emission of individual train compositions.The Empa researchers need this data to calculate how noise propagates in the direction of nearby residents. The intensity of train noise depends on many factors such as the kind of train passing, its speed, whether cliffs or buildings reflect the noise, the construction of the track bed, the local topography, and – not least – the weather. Only if all these parameters are taken into account in the computer simulation it is possible to quantify the noise pollution levels accurately.