Acoustic Resonator for Mitigation Actions on Underground Railway Lines

Noise pollution caused by underground railway lines is particularly strong in open sections, where levels of noise equal to or superior to noise produced by traffic reach the surrounding receivers. In order to minimise the acoustic impact, it is not always possible, for aesthetic or structural reasons, to build ad-hoc noise barriers. It is therefore necessary to consider less invasive actions that can reduce noise close to its source, taking into account the fact that noise produced by train transit is mainly due to the wheel-track contact. In this paper an acoustic resonator is presented, designed to reduce noise produced by the wheel-track contact in the Rome underground railway lines. Considering that the train emission spectrum, measured close to the permanent way, has a peak around 350 Hz, the acoustic resonator was tuned on this frequency interval and designed using the space between the safety gangway and the support plane of the railway line. The value of the resonator’s absorption coefficient was verified experimentally on a prototype built for the purpose.