Empa Explores Noise Generation from Passenger and Freight Trains

At Empa, acoustics experts have been exploring for years how noise is generated by passenger and freight trains – and which technical and structural measures are particularly effective against it. Their theoretical and practical findings have now been incorporated into the project “SILVARSTAR”. The result is a simulation tool for railway noise that can also be helpful in practice.

(Dübendorf/St. Gallen/Thun) For residents near railway lines, it is often bothersome – and for professionals who want to help them, it is such a multifaceted challenge that there should actually be a plural of “railway noise”. Rolling noises from steel wheels on rough or smoother tracks, braking sounds at different frequencies, engine noise, aerodynamic sounds… – all of this is dampened or influenced by noise barriers, embankments, the nature of the ground beneath the tracks, and also by the environment in which the sound waves propagate.

How complex these acoustic effects of rail traffic are is known by Empa researchers led by group leader Reto Pieren from the “Acoustics / Noise Reduction” department from practical and theoretical experience. For years, they have been exploring the phenomenon with measurements, simulations, and validations: insights that culminated in the two-year EU project “SILVARSTAR” with many partners (see info box). Pieren recently presented the results at the “forum acusticum” conference in Turin: an acoustic simulation of railway noise in various forms – audible and experienceable with the help of virtual reality.

Such tools for “auralization” exist sporadically as prototypes in research, but they are not yet available in the practical fields of planning and noise protection. The “complete package” SILVARSTAR aims to change that – thanks to the combined knowledge of many experts. While the Empa team, which led the project in the simulation, incorporated its acoustic expertise from numerous projects, experts from the “University of Southampton” and the Zurich company Bandara VR GmbH contributed valuable know-how to develop a user-friendly system. The widely used software “Unity” for professional game developers served as a basis for this.

A Tool That Laypeople Can Use

The goal was ultimately a tool that laypeople could use. For example, transport policymakers who want to assess the impacts of a future railway line. How they experience such virtual pass-bys is exemplified by a video of pass-bys that can be found on the SILVARSTAR website of Empa: For a single route, several scenarios can be compared, for example with train types ranging from freight trains to regional trains to the ICE, with high or low noise barriers, specific wheel and damping types that also have an audible impact on railway noise, and many other factors. And because the environment also plays a role, users can choose between “city” or “countryside” or select a ground-level or elevated position, such as on a balcony.

Behind these possibilities are complex algorithms in a physics-based computational model that does not generate acoustic signals from archived sound files but calculates and generates them individually – for hundreds of noise sources and influencing factors, depending on the complexity of the scenario. This also posed challenges for the Empa team. The great variety of influences allows for realistic simulations. However, it also required reducing the web of algorithms sensibly to the essentials – also considering the necessary computation time: A modern PC needs up to three hours for a pass-by of a 500-meter freight train to make its noise emissions audible under different conditions.

The Effort is Worth It

But the effort is worth it, as the validation of the system showed. The graphics of the synthesized noise profiles are very close to measured comparison values and are even partially identical. Subjective impressions were provided by demonstrations at traffic technology fairs such as “InnoTrans” last year in Berlin: Visitors attested to the simulation’s high credibility and showed great interest in the application of the virtual “railway noise game”.

For interested parties, the download of the tools along with a license agreement for non-commercial purposes is possible via the SILVARSTAR website of Empa. “The first applications of the simulation are already beginning,” says Empa researcher Reto Pieren, “we are very satisfied with the results and expect numerous applications in the future.”

International Project with EU Funding

The European research project “SILVARSTAR”, which ran for just over two years, was funded under the EU program “Horizon 2020” by “Europe’s Rail”. In addition to Empa, the project consortium included industrial and academic partners from five European countries: Vibratec (France, coordination), Wölfel Engineering (Germany), the “University of Southampton” (England), KU Leuven, and UNIFE, the “Union of European Railway Industries” (both from Belgium). In addition to simulating railway noise, the project also developed models for ground vibrations caused by train traffic.

Photo: © Empa / Caption: Experience freight train pass-bys playfully: The monitor shows what the user sees in three-dimensional virtual reality – with realistic railway noise exactly at their position.