Validation and Calibration of a Fatigue Assessment Tool for Railroad Work Schedules, Final Report
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2007-05-11
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Abstract:This report summarizes the results of a project to demonstrate a method to validate and calibrate a fatigue model. The project examined 30-day work histories of locomotive crews prior to 400 human factors accidents and 1000 nonhuman factors accidents. A biomathematical fatigue model estimated crew effectiveness (the inverse of fatigue) based entirely on work schedule information and opportunities to obtain sleep. A reliable linear relationship existed between crew effectiveness and the risk of human factors accidents (r = - 0.93), but not for nonhuman factors accidents. A reliable time of day variation occurred in human factors accidents (r = 0.71). The risk of human factors accidents was elevated at any effectiveness scores below 90 and increased progressively with reduced effectiveness. At an effectiveness score ≤ 50, human factors accidents were 65 percent more likely than chance. Human factors accident risk increases reliably when effectiveness goes below 70, a value that is the rough equivalent of a 0.08 blood alcohol level or 21 hour wakefulness following 8-hour sleep. Below an effectiveness score of 70, accident cause codes indicated the kinds of operator errors consistent with fatigue, confirming that the relationship between accident risk and effectiveness was meaningful. Consistent night workers were estimated to spend a majority of time working between effectiveness 60 to 80; a significantly larger proportion of accidents had human factors causes (37%) compared to day workers (27%).
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