Chapter 6 148 The acoustic characteristics of the warning signals in Dutch locomotive cabins do not seem to optimally facilitate engineers in performing their job safely and effectively, especially if hearing loss is present. The most prominent signal peaks of the warning signals include the spectral elements that are commonly affected most strongly by noise-induced hearing loss or age effects, respectively, between 2000 and 4000 Hz and 4000 and 8000 Hz (Van der Hoek-Snieders et al., 2021). We therefore recommend to investigate the possibility to modify the acoustic warning signals to make them more robust against hearing loss and background noise. This can be done, for example, by using broadband signals rather than tonal signals (Nélisse et al., 2011) or by adding more low frequency sound components (ISO, 2003). However, even if such an optimization has been realized, it still remains important to assess an individual locomotive engineer’s auditory fitness for job to ensure driving safety and effectiveness. By assessing signal detectability in terms of the SNR50, we made use of a quantitative performance level. This is in line with the recommendation that a measurement used for determining fitness for job must be accessible in terms of a quantitative performancemeasure to provide fine discrimination between individual performance levels (Payne & Harvey, 2010). The quantitative performance levels can be used to determine a set of standards for the signal detection test, such as minimum standards for job performance in each train type. Eventually, the signal detection test will result in one of the following conclusions: (1) the engineer is capable to safely perform the job, (2) accommodations are needed to safely perform the job, such as hearing aids, or (3) the engineer is incapable to perform the job safely. For drawing these conclusions, future research is required to establish the cutoff points. Precaution is required when hearing aids are required for sufficient signal detectability. Due to the high noise levels in Dutch train cabins, hearing aids should be well limited to avoid over-exposure (Dolan &Maurer, 2000). The signal detection test under study is task and job specific, but it does not replicate the job task with regard to all job characteristics. The only task of the test is to detect the acoustic signals, rather than combining detecting signals with other tasks, such as driving safely and communicating with others (Zoer et al., 2014). Also, the signal detection test assesses the signals one by one, whereas an engineer should distinguish the DSD and ATP signal during normal operation. Finally, we used an up-down procedure to determine the SNR50, whereas in the real work situation, the warning signals need to be detected at a certain, predefined level. Due to the
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