The body's natural biological clock has
a major influence on sleepiness, as these accidents peak around 02:00h-07:00h
and 14:00h-16:00h, when daily sleepiness is naturally higher [ 1 ].
Sleep-related vehicle accidents are more evident in young male drivers
in the early morning and among older male drivers during the mid-afternoon,
as the afternoon "dip" tends to become more apparent as one
gets older [ 2 ].
Of course, young men are more likely to be on the road in the early morning.
However, as the effects of sleep loss and sleepiness are more profound
in younger than in older people, which young men tend to deny, they are
at a much greater risk when driving during the small hours.
In taking a break (e.g. 30 minutes), what should the sleepy driver
We have found that exercise (e.g. brisk walking) is of little use [ 6
Short naps (less than 15 minutes) are very effective [ 7 ], as is caffeine
(150mg - as in about 2 cups of coffee or two cans of 'functional energy
Better still, take this caffeinated drink and then take the nap [ 8 ].
Caffeine takes 20-30 minutes to be absorbed and act on the brain; hence
there is the opportunity for a nap.
Caffeine (200mg) in the form of a beverage is particularly good for the
early morning driver having had little sleep that night [ 9 ]. These
findings from Phase 1 and 2, concerning caffeine and naps, have been
incorporated into the latest edition of the Highway Code.
Our research has indicated that:
1. Sleep-related vehicle accidents (SRVAs) are more likely to result
in serious injury than the 'average' road accident.
2. Few accidents we investigated seemed to have alcohol as a contributory
3. Men aged 30 years and under are more likely to have a SRVA, and seem
to be at a higher risk.
4. Drivers from skilled manual occupations are also more likely to have
a SRVA, probably because of a higher exposure to driving.
5. Driving between 02:00h and 07:00h presents a particular risk for SRVAs,
as this is when one's 'body clock' is in a daily trough. There is another,
smaller trough between about 14:00h and 16:00h.
6. Low traffic density is probably not a major risk factor for SRVAs.
It is the associated factors, such as driving in the early morning, during
the 'trough', when traffic density also happens to be low.
7. About 40% of SRVAs are probably work-related, inasmuch as they involve
commercial vehicles (HGVs, light goods vehicles and vans etc).
8. Sleepy drivers are aware of their sleepiness, particularly when they
reach the stage of 'fighting sleep' (i.e. doing things to keep themselves
awake, such as winding down the window).
9. Reaction time devices are of little practical use in detecting driver
10. Drivers already chronically, mildly sleepy (e.g. due to chronic levels
of sleep disturbance or insufficient sleep), are more vulnerable to any
transient, additional sleep loss, and may not so easily perceive this
increase in sleepiness.
11. Caffeine (150mg) is an effective countermeasure to sleepiness, as
is a short (less than 15 minutes) nap or doze.
The two combined together (caffeine in the form of a caffeinated drink,
then a nap) are particularly effective.
The efficacy of these treatments will depend on the magnitude of the
sleepiness. Even 'relaxing with the eyes closed' is worthwhile.
12. Sleep related accidents should no longer be viewed as 'accidents'
but as road crashes due to easily preventable human error.
13. We feel strongly that driver education, linked to greater public
awareness of the potential dangers of sleepiness, together with greater
employer responsibility with regard to their employees' fitness to drive,
present the best approaches for reducing sleep related crashes.
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
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
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.
this latest Report from the Department for Transport
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