The predominant contributor to railway noise, even for train speeds reaching 350 km/h, is rolling noise, generated primarily through vibrations of both wheel and track. Of these two components, the noise emitted by the rail is typically the most significant across the mid-range frequencies spanning from about 400 Hz to 2 000 Hz. The surrounding structures, i.e., the track structure and ground surface underneath, as well as the wheel and train body above, may affect the acoustic characteristics of rail radiation, and hence the estimation precision of rolling noise. The geometrical influence of the nearby structures on the noise produced by a railway rail is investigated systematically by using the boundary element method with adaptive order in three dimensions. Comparisons are also made with measurement data. These adjacent structures are shown to affect both the sound power and the sound pressure spectra, especially below 2 kHz. The wheel has a negligible impact on the rail radiation, but the proximity of the slab or ballasted track structure and the car body exerts more pronounced effects. Their influence is larger for a ballasted track configuration than for a slab track design due to the acoustic absorption of the ballast bed. Approximate formulae are proposed for the directivity of the rail in situ when it is excited vertically, which can be used in simulation models of practical rolling noise.
Zhang et al. (2026) studied this question.