LAUSR

Abstract Conventional railway track is supported by a layer of crushed stones known as ballast. In recent years concrete slab tracks have been introduced which have been used widely in the construction of high-speed lines. However, a particular concern is that slab track is considered to be noisier than ballasted track. In order to investigate the differences in the noise radiation characteristics of ballasted and slab tracks, the TWINS model for rolling noise has been updated. Differences are included in the sound radiation of the rails and sleepers due to the presence of absorptive or reflective ground and the effect of the ballast vibration on the sound radiation of the sleepers is taken into account. The effects of the ballast absorption under the train on the sound propagation are also considered. To calculate the sound radiation from the slab itself, a waveguide finite element/boundary element method is used, which includes the supporting ground. The slab vibration is shown to be the dominant noise source only up to around 100 Hz, whereas it is negligible at higher frequencies. Results are presented for two ballasted tracks (one with stiff rail pads and the other with soft pads) and one slab track, and compared with measured data. Finally, the sound radiation from the various tracks are compared for equivalent situations. The results are found to depend on the assumptions made, particularly in relation to the track decay rates and roughness spectra; the ground conditions adjacent to the track also affect the sound pressure spectra below 1 kHz.