A track-independent vehicle indicator for ground-borne noise and vibration emission classification

Abstract

Ground vibration from railways is increasingly recognised as a source of annoyance to lineside residents. However, in contrast to airborne noise, there are no standard test procedures to quantify the vibration emission of trains. This is compounded by the fact that measurements of vibration are highly sensitive to the properties of the test site. Here, to help overcome this, a ‘track-independent vehicle indicator’ (TVI) is proposed that can be used to classify railway vehicles in terms of their ground-borne noise and vibration emission. Two different formulations of TVI are proposed, one related to feelable ground-borne vibration and the other to ground-borne noise. The proposed TVIs are based on the force density at the railhead, which may be obtained indirectly from measured ground vibration due to train passages together with a measured line source transfer mobility at the test site. Corresponding frequency weightings are defined to mimic the sensitivity of human response to ground vibration or ground-borne noise. Each TVI is a single number quantity, defined as a sum over all relevant frequency bands of the frequency-weighted force densities. The proposed performance classification of different vehicles can be achieved by comparing the relative differences of their TVIs. The force density is chosen as the basis of the TVIs because, in contrast to the vibration levels, it is relatively independent of the test site. Nevertheless, some restrictions should be applied to the site to avoid undue influence from the track or ground properties. A transposition procedure can also be used to convert results to a standard situation to reduce this influence. A series of test cases is used to demonstrate the potential of the TVIs to classify railway vehicles in terms of their ground-borne vibration and noise emission.