Noise in the environment is increasingly perceived as a nuisance with potential adverse effects on public health. The European Commission is developing policies to control noise, and much attention is focused on the transport sector. Effective action requires standard methods to measure noise, in order to identify problem areas and evaluate abatement methods.
The main objective of METARAIL was to develop and improve techniques for measurement of railway exterior noise, for the purposes of type-testing of rolling stock, monitoring of ambient noise and diagnosis of the sources of noise.
Thirteen techniques were studied in the project, including the testing of four new ones. Hardware and/or software were developed for six techniques.
Some of the techniques have been put forward as potential improvements to the ISO 3095 standard for railway exterior noise type testing. The changes are intended to give greater accuracy and reproducibility, especially when comparing measured data between different sites.
These methods were applied in a series of tests with a special test train at sites in four countries. Due to the improved procedures, measurement results were reproducible within a range of +/- 2 dB(A), which is a substantial improvement on the previous range of +/- 5 dB(A) or more. This was only possible due to accurate assessment of rail roughness, accurate speed control and careful monitoring of site-specific characteristics.
New methods for separating vehicle and track noise were demonstrated, such as a low-noise reference vehicle method and improved acoustic antenna techniques. The procedures were shown to be capable of quantifying the noise reductions due to low noise solutions such as improved braking systems and bogie shrouds. For example, it was possible to show which part of the noise reduction was due to lower roughness and which was due to shrouds.
In the tests, cast-iron block-braked wagons were the noisiest, followed by sintered metal block-braked wagons (about 6-8 dB(A) quieter) and then disc-braked and shrouded wagons (a further 4 dB(A) quieter). The largest reduction was due to lower wheel roughness, which was comparable to the rail roughness levels at most of the test sites. The bogie shrouds reduced vehicle noise by 4-7 dB(A), but the effect was limited by the remaining track noise contribution.
The METARAIL project maintained an interaction with the European Rail Research Institute's Advisory Group on Noise and Vibration, the Union International de Chemin de Fer's Task Force on Noise, the CEN standards body and other stakeholders. The project results have already in part been fed into a new draft of the ISO standard, prEN ISO 3095 (exterior noise type testing of rail vehicles), increasing its reproducibility and enabling better assessment of noise control measures for rail vehicles and tracks. The results of METARAIL are also serving as input to an EU working group on railway noise, which is advising on impending noise legislation (via Interoperability Directives) on high speed and conventional rail systems.
In the longer term, the project results will assist national authorities in determining measures needed for compliance with future Community legislation on noise.