Pergamon Accid Anal. and Prev.. Vol. 29. No. 4, pp. 489 494. 1997 C 1997 Elsewer Science Ltd All rights reserved. Printed in Great Britain oooi-4575:97 Sl7.00 + 0.00 PIkSOOOl-4575(97)00028-6 zyxwvutsrqponmlkjihgfedcbaZYXWV MOTOR VEHICLE ACCIDENTS, FATIGUE OPTIMISM BIAS IN TAXI DRIVERS JAMESR.DALZIEL* and R.F.SOAMESJOB Department of Psychology, University of Sydney, Sydney 2006. Australia AND Abstract-Fatigue-related variables and their relationship with accident involvement were examined in a group of 42 Sydney metropolitan taxi drivers across a 2-year period. Advantages associated with the study of this group of road users include their important role in public transport, long hours spent on the road, job-related controls of exposure through shift patterns and the ability to verify accidents with company insurance records. Number and length of breaks, employment type, falling asleep at the wheel and a variety of other job-related and attitudinal variables were surveyed. Results provide basic data on fatigue-related aspects of the job of taxi driving. Driver time-on-the-road is often considerable: 67% of those surveyed drove at least 50 hours per week, yet time off in long shifts (up to 12 hours) was often short (as low as 3 minutes, with an average of 37 minutes). Self report of accidents proved reliable against insurance company records. A significant negative correlation between total average break time and accident rate was observed. Optimism bias was present for a variety of driving-related questions, including the ability to drive safely while fatigued. 0 1997 Elsevier Science Ltd. Keywords-Fatigue, Taxi drivers, Optimism bias, Motor vehicle accidents INTRODUCTION One of the major factors in traffic accident causation is the effects of fatigue on drivers, but the contribution of fatigue to accidents is often underestimated in official reporting (Corfitsen, 1994; Brown, 1994). In certain types of accidents (particularly nighttime ran- off-road single vehicle accidents) fatigue is thought to be the primary causal factor (Brown, 1994). Fatigue is a general term commonly used to refer to the experience of being ‘sleepy’, ‘tired’ or ‘exhausted’ (National Aeronautics and Space Administration-hereafter NASA, 1996). Fatigue may be conceptualized as both a psychological and physiological experience (Brown, 1994; NASA, 1996), although Brown argues that the essential ele- ment is the “subjectively experienced disinclination to continue performing the task at hand” (p. 302). Fatigue can result from sleep loss and circadian rhythm disruption (NASA, 1996). In the case of sleep loss, alertness and performance are diminished by insufficient sleep for a given individual, especially where sleep loss occurs across several nights, and accumulates as a ‘sleep debt’. Sleep loss can result in effects such as slowed reaction time and lack of concentration, as well as poorer decision-making and worsened mood (NASA, 1996). Disruption of circa- *Corresponding author. 489 dian rhythms occurs when the body’s ‘internal clock’ is affected by changes in timezone, or changes from day to night shifts. The effects, which are similar to sleep loss, last until the body’s clock readjusts to the new setting. The NASA Fatigue Resources Directory also notes that, “when circadian disruption and sleep loss occur together, they can interact to compound their adverse effects”. However, there is an additional potential source of fatigue: the task being performed. While laboratory studies which involve sleep loss followed by some form of test (such as a reaction time task) may not need to consider the effects of the fatigue induced by the test itself, this is not the case in prolonged driving. As Crawford ( 196 1) points out, there are two impor- tant sources of fatigue in driving: first, the fatigue caused by driving itself (especially when this is for a prolonged period); and second, fatigue from other sources (these ‘other sources’ could include sleep loss, circadian rhythm disruption and the effects of other work performed before driving). All of these are relevant when examining the effects of fatigue on driving. An important distinction also exists between muscular fatigue resulting from hard physical work (e.g. labouring), and ‘skill fatigue’, which is more related to the effects of prolonged concentration and vigilance in performing a fairly complex task, such as driving (Brown, 1994; Crawford, 1961). Studying the role of fatigue in driving behaviour