Brigitte Hafner
is a communicator in the Rail Cargo Group
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Research & Development

Whisper brakes

Quietly running trains

Imagine being woken up abruptly in the middle of the night. The reason: a freight train thundering past. That will soon change. By the end of 2021, tourists as well as people living alongside railway lines should be significantly relieved from the noise of freight trains. That’s because freight wagons are being retrofitted with low-noise brake systems with modern brake pads made of composite material for an audible reduction of noise impact.

Freight trains travelling at high speed are unpleasantly noisy, particularly for local residents and guests in tourist regions. The biggest noise source is the rolling sound of freight trains and comes from the point of contact between wheel and rail. The noise is caused by rough and worn running surfaces of the wagons coming into contact with rough rails. The intention now is for all freight wagons to be equipped with so-called whisper brakes. Brake pads made of rubber and copper composites are used for this purpose. These are elastic and therefore lower-noise materials than were used on older, metallic, grey cast iron brakes. While the running surfaces of wheels with grey cast iron brakes are roughened during each braking process, wheels fitted with whisper brakes remain smoother. That’s why freight trains with, for example, composite pads (K-pads) or the LL-pads (“low noise, low friction”) approved in 2013 cause less noise, because their smoother surface makes rolling noises so much quieter.

When a reduction in noise becomes audible

Transport Minister Jörg Leichtfried, Governor of Carinthia Peter Kaiser and State Commissioner for Transport Rolf Holub themselves got an idea of the noise relief measures at the end of September on a demonstration ride in Krumpendorf am Wörthersee on board a freight train, half of which was fitted with modern brake pads made of composite material. The difference was clearly audible. It amounts to up to ten decibels. This means that the trains sound almost half as loud as conventional wagons fitted with grey cast iron brakes.

The Rail Cargo Group has already made 40 percent of the wagons used in Austria quiet. All new wagons of the Rail Cargo Group are already being delivered with modern, quieter brakes. By the end of 2021, over 90 percent of our vehicles, most of which we use in Austria, will have been retrofitted with low-noise brakes and quiet pads.

Präsentation neuer Bremssysteme für Güterwaggons durch BM Jörg Leichtfried, LH Peter Kaiser und LR Rolf Holub
©fritzpress

When unevennesses in the track system turns into noise

But freight wagons and their brake systems are not the only parts that produce noise. Passing trains create tiny slip waves in the rail surface or deformations in the rail head, which represent a noise source and also cause vibrations that can stress both vehicles and the track superstructure. A rail grinding train – an approximately 70 metre-long, 2,500 bhp special machine with 24 grinding motors – then comes along and removes the fine irregularities in the rail surface. This involves grinding off and removing the topmost layer of around 0.3 millimetres. The running surface is made smooth and contact between the wheels and rail is optimised. The interaction between wheel and rail then runs again as if freshly lubricated.

A blessing for the people living alongside the railway line, since the new rail profile significantly reduces the noise produced by a passing train. Smooth running surfaces also mean a quieter, more pleasant travel experience for train passengers and thus a more comfortable journey. The service life of the tracks is also extended many times over.

A feast for the population’s ears

The measures also allow the population living alongside rail corridors used by freight trains to breathe a sigh of relief. However, the issue doesn’t stop at Austria’s borders. Rather, the aim is to reduce railway noise at its source, because only when all European railways and private wagon owners run on modern brake technology can decisive relief be guaranteed. And this will affect all of Europe. The goal is to make Europe’s most environmentally friendly freight traffic much quieter and hence even more attractive. Because we protect the environment with each tonne transported by rail. Freight moved by rail releases 18 times less CO2 into the environment compared to road transport.

On the initiative of the Ministry of Transport, the conversion to so-called whisper brakes is in any case rewarded with a whisper bonus on the rail toll as way of motivating transport companies to make the switch.