Driver sleepiness (No.21)

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APPENDIX

RECENT PAPERS

Horne J & Reyner L (1999) Sleep related accidents: a review. Occupational & Environmental Medicine, Vol. 56: 289-294. (Impact factor = 2.0)

Summary
Falling asleep whilst driving accounts for a significant proportion of vehicle accidents under monotonous driving conditions. Many of these accidents are work-related (e.g. trucks, goods vehicle and company car drivers). Time of day (circadian) effects are profound, with sleepiness being particularly evident during night-shift work, and driving home afterwards. Circadian factors are as important in determining driver sleepiness as is the duration of the drive, but only the latter is built into legislation protecting professional drivers. Older drivers are also vulnerable to sleepiness in the mid-afternoon. Possible pathological causes of driver sleepiness are discussed, but there is little evidence that this factor contributes significantly to the accident statistics. Sleep does not occur spontaneously without warning. Drivers falling asleep are unlikely to recollect having done so, but will be aware of the precursory state of increasing sleepiness; probably reaching a state of fighting off sleep prior to an accident. Self awareness of sleepiness is a better method for alerting the driver than in-vehicle automatic sleepiness detectors. None of the latter are of proven reliability and most have shortcomings. Putative countermeasures to sleepiness, adopted during continued driving (e.g. cold air, use of car radio) are only effective for a short while. The only safe countermeasure to driver sleepiness, particularly when the driver reaches the stage of fighting sleep, is to cease driving and, for example, take a 30 min break encompassing a short (

Reyner LA & Horne JA (2000) Early morning driver sleepiness: effects of 200mg caffeine Psychophysiology, Vol. 37: 251-256. (Impact factor = 3.00)

Summary
Sleep-related vehicle accidents are prevalent early morning, especially in younger drivers. In two independent studies following a night of either restricted or nil sleep, young experienced drivers drove for 2h (0600-0800h) continuously in an immobile car on an interactive, computer-generated dull and monotonous roadway. This followed ingestion (at 0530h) of 200mg caffeine (=2-3 cups coffee) Vs placebo, counterbalanced, double blind. Driving incidents (lane drifting), subjective sleepiness, and 4-11Hz EEG activity were logged. Study 1 (sleeping 0000-0500h): caffeine significantly reduced incidents and subjective sleepiness throughout the 2h drive, and EEG power for the second 30min period. Study 2: (no sleep) sleepiness profoundly affected all measures, and driving was terminated after 1h. Nevertheless, caffeine significantly reduced incidents for the first 30 min and subjective sleepiness for the hour. This caffeine dose, feasibly taken via coffee, effectively reduces early morning driver sleepiness for about 30min following nil sleep, and for around 2h after sleep restriction.

 

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