Noise control design of railway vehicles–Impact of new legislation

Type testing specifications can affect the design considerations for a rail vehicle. It is shown with illustrative examples how low-noise design features optimized for the type test condition may have very limited effect for normal operation. The type test conditions in the new European legislation Technical Specification for Interoperability-Conventional Rail (TSI-CR) for noise emission from interoperable rail vehicles is used as a basis. The purpose of a pass-by noise type test is to certify the rolling stock but the track is in many situations both the dominant excitation and radiation source. In the TSI-CR a stringent track specification is defined to keep the track noise contribution low and to promote reproducibility between test sites. It is shown by simulations with the TWINS software that the ranking of noise sources may be different on a type test track than on a typical operational track. This may lead to a demand to introduce noise reduction features on the vehicles that have a small effect on operational track. As two examples, the introduction of wheel absorbers and bogie skirts is investigated. The inaccuracies in the present standards for rail roughness measurement and the consequence in terms of uncertainties in noise emission are highlighted. For rail vehicle type tests under stationary and accelerating conditions, the track properties are irrelevant but the operating modes of auxiliary equipment and cooling fans are crucial. It is shown that the consequences of either specifying a typical load cycle or a worst-case scenario are considerable due to different ranking of sources. Consequently, the focus for the engineering work can in such cases be devoted to systems that only dominate in extreme cases and do not contribute to the noise emission during normal operation.