Railways are becoming increasingly market-driven. Consequently, it is important that passengers are provided with a comfortable environment that reflects the operator's desired image for the service. A major factor in determining how passengers perceive the environment within trains is the level and nature of sound to which they are exposed. Unfortunately, the subject of noise within railway vehicles has had less attention in recent years, and is therefore less well developed, than external "environmental" noise. Two specific areas that merit investigation are methods for its quantification and assessment. A variety of criteria are used for assessing the noise environment within buildings, and may be considered appropriate for the quantification of internal train noise. These include "noise criteria" (NC), "preferred noise criteria" (PNC), "noise rating" (NR), and "room criterion" (RC). Recently, the automotive industry has also been using loudness level. Simple descriptors, such as the A-weighted sound level, have not been found to correlate well with perceived acoustic comfort. A complicating factor when considering internal rail vehicle noise is that its level and quality is not constant, with significant variability likely to occur over the duration of a journey. This difficulty is compounded by acoustic spatial variation within a vehicle. The paper considers the problems inherent in the quantification of noise within rail vehicles, and in the determination of the relationship between this noise and passenger response. Methods by which these problems may be overcome are discussed, drawing on real data and on long experience of study in this field.
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