SNCF researchers have already reduced noise by 10 decibels in 20 years. They are aiming to claw back another 5 by 2012 and 10 by 2020.

Getting to the heart of the matter.At speeds up to 80 kph, the engine and ventilation systems produce the most noise. From there to 300 kph, the wheel noise is the loudest. At speeds of 320 kph, aerodynamic noise reaches similar levels to wheel noise. There are a whole range of noise sources, so reducing the decibels involves a combination of different solutions. SNCF Research has developed a range of solutions, such as optimising the diesel engine cooling fans and fitting noise absorbers on both the tracks and the wheels. Vamppass software, designed in partnership with the CNRS, is used to synthesize train noise and indicates which sources should be dealt with first. Combining all these solutions does the rest, and has cut noise fivefold!

Focus on brakes. Studies in the Paris region have shown that the brake shoes are a key factor in the noise produced by Transilien trains. Time to do away with those iron shoes! On 85% of the fleet, they have been replaced by shoes made of composites specifically designed by SNCF research labs, reducing noise by 8 to 10 decibels. The issue of screeching brakes on high-speed trains is now being researched as part of the PREDIT programme. Noise sources have been identified and different brake linings have been tested. The research continues...

Troublesome bridges. There are 900 metal railway bridges in France. At low frequencies, noise comes from the surface of the bridge; at high frequencies, it comes from the tracks. The solution that SNCF has put to RFF is an innovative mix - a combination of an optimised track anchoring system, noise screens and dynamic absorbers on the track and bridge floor succeed in silencing bridges as the train crosses.

The next sound barrier.As part of the PREDIT research programme, the RFF has commissioned SNCF researchers to work on protecting local residents from the noise of freight trains. Rather than building ever higher barriers, they have developed a new generation of screen. The new screens are much lower than the straight concrete walls which run alongside roads and railways, and do not cause an eyesore. The noise is absorbed through an innovative geometrical design. It can also be equipped with diffractive ridges, "scattering" the sound waves for maximum effect. SNCF researchers have drawn on the work of the CSTB to develop a piece of software which calculates the characteristics of the perfect noise barrier. The first screen should be built in 2010, meeting expectations of local residents and the RFF, which is investing heavily in reducing noise black spots.

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