The U.S. National Transportation Safety Board investigated 113 heavy-truck accidents to determine “the role of specific factors, such as drivers' patterns of duty and sleep, in fatigue-related heavy truck accidents” (NTSB, 1995a). For a number of reasons, we believed that a re-analysis of this data, with a different set of variables, might yield a more complete picture regarding the nature of fatigue-related accidents and their causes. Specifically, principal components analysis was employed to determine the underlying factors that contributed to accidents where fatigue was determined to be the primary cause. In this analysis, two principal components were extracted that dealt with (1) the nature of the driver's sleep periods and level of experience, and (2) aspects of the driver's work periods. Subsequent cluster analysis demonstrated that the cases could be divided into two distinct accident modes or types: those with and those without regular sleep/work patterns. Drivers with generally regular sleep/work patterns appeared to develop fatigue while on the job, while those with irregular sleep/work patterns appeared to arrive at the job already fatigued. In conclusion, the variables which contributed to fatigue in the NTSB report were found to contribute to fatigue in the present analysis, but not to the same extent in all cases. Some of the variables that influenced driver fatigue in one of the clusters (or accident modes) had no effect on the other. These different accident modes should be considered when examining the effect of a given variable on fatigue.
Statistical description of heavy truck accidents on representative segments of interstate highway
