Chapter 5 116 hearing assessments when hearing thresholds are measured at 25 dB HL or lower on the frequencies 1000, 2000, and 4000 Hz at the better ear. When a driver passes the hearing screening, sufficient hearing for safe and effective job performance is concluded. It is thus assumed that train drivers with hearing thresholds below 25 dB Hearing Level (HL) are capable of signal detection in the train cabin. This assumption has not yet been validated. To evaluate the detectability of warning signals in a specific work-setting, the signal level should be taken into account (Edworthy, 1994; Giguère et al., 2008). If the signal level is too low, the warning signal cannot attract proper attention. According to ISO7731, a warning signal level is advised to be at least 65 dBA to ensure audibility (ISO, 2003). If the level is too high, the sound can be distracting, can hinder speech communication, or even can cause startle reactions (Edworthy, 1994; Giguère et al., 2008). ISO 7731 therefore states that the maximum sound level of a warning signal should not exceed 118 dBA (ISO, 2003). Additionally, the background noise at each workplace should be taken into account, including the level, spectrum, and type of the noise (Edworthy, 1994; Giguère et al., 2008). A train cabin is a noisy working environment with A-weighted estimated noise levels between 70 and 93 dBA (Lie et al., 2013; Peng et al., 2019). Driving speed can influence the ambient noise level, since the overall exterior sound emission increases with driving speed and several of the internal noise sources depend on driving speed, such as the motor and cooling ventilator (Kurze et al., 2000; Pronello, 2003). Noise levels have been shown to differ between Italian train types (Pronello, 2003), but this has not yet been investigated for Dutch trains. Furthermore, it is unknown if the effect of driving speed on the noise level is similar in different train types. Computerised tools have been developed to model the expected signal detectability in a specific work setting (Giguère et al., 2008). These models are often based on masked thresholds, defined as the signal level that is just detectible in the presence of the workplace noise (Giguère et al., 2008; Zheng et al., 2007). In accordance with ISO 7731, a signal level of 10–15 dB above masked threshold has been proposed to warrant signal detectability (ISO, 2003; Laroche et al., 1992). There is no model available yet that computes the detectability of the warning signal in the work situation of Dutch locomotive engineers. We therefore aim to specify the acoustic characteristics of the warning signals and the noise levels present in Dutch train cabins and to evaluate the effectiveness of these warning signals when presented to normally-hearing locomotive engineers.
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