The purpose of this study was to investigate the causes of fatigue among rail staff by analysing qualitative data and conducting an online diary study. It had a closer look at the experience of fatigue among rail staff and brought a more detailed blueprint picture of fatigue and its causes in the rail staff's real-life. Study 1 analysed 133 responses of qualitative data from rail staff, and Study 2 was a diary study examining fatigue and its related risk factors before and after work, on the first and the last day of a working week in 19 rail staff. The findings from the two studies, using different methodologies, showed similar results that fatigue was a result of heavy workload, long working hours, shift-work, and insufficient rest and sleep. Fatigue before work mainly resulted from sleep quality, length of sleep, and the time spent on commute, while fatigue after work resulted from the workload and shift type. Evidence has demonstrated that overtime work, specific shift patterns, insufficient rest days between opposed shifts, and poor timing of breaks during work were also associated with fatigue.