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Sleep laboratories around the world, including our own at Loughborough
University of Technology, are finding that an alarming number of drivers
on motorways may be falling asleep at the wheel. Although researchers have
difficulty in knowing for certain whether an accident has been caused by
sleepiness, it appears that a driver who is on the road between 4 am and
6 am is about 10 times as likely to have a sleep related accident as someone
who is driving in the middle of the morning or early in the evening. Some
British police forces have become sufficiently concerned to launch campaigns
to alert the public to the danger. Leicestershire police, for example, consider
sleepiness to be the cause of 20 per cent of accidents on motorways and
in the summer of 1990 ran a campaign with the slogan ‘Stay Awake, Stay Alive’.
Major motor manufacturers such as Ford and Renault are taking the issue
of driver sleepiness very seriously, and are investigating ways of incorporating
sleepiness detectors and alarms into their vehicles.

However, British government bodies responsible for road safety have
not initiated any studies into the problem of sleepy drivers on motorways.
The Department of Transport claims that it is ‘aware of the problem’, but
does not regard it as a high-priority issue and is not planning to support
any relevant research apart from a general study on ‘driver behaviour’.
The department has no figures on the number of accidents caused by driver
sleepiness and says it doubts whether reliable statistics can ever be obtained.

Unfortunately, the issue is clouded by the fact that many motorway accidents
that might be caused by sleepiness are categorised under other headings,
such as ‘inattention’, ‘failed to look or see other vehicle’ and ‘misjudged
speed/distance’. Figures collected in the 1970s by the Transport and Road
Research Laboratory list the cause of 20 per cent of all road accidents
as ‘perceptual errors’. ‘Fatigue’ was specified in only 2 per cent of cases.
However, few investigators inquire further to discover just why a driver
was not attending, failed to look or made errors in perception. For various
reasons, including the fear of prosecution and possible difficulties with
insurance claims, drivers are reluctant to admit to falling asleep, but
are more willing to admit to ‘inattention’. When these rather vague responses
are examined thoroughly, sleepiness often emerges as the true culprit.

Driving on a road as dull as a motorway exacerbates sleepiness in a
driver who is already sleepy. But how can we tell if an accident on a motorway
has been caused by sleepiness? There are some very strong pointers. If an
accident involves only one vehicle, which runs off the road into the central
crash barrier, the embankment, a tree or a bridge, then sleepiness is likely
to be the cause, especially if there are no skid marks or other signs of
braking. A driver who is alert to an impending crash grips the steering
wheel and suffers different injuries from someone who is asleep and holding
the steering wheel loosely. This pattern of injury, combined with an absence
of skid marks on the road, also suggests that the driver was asleep in accidents
where one vehicle runs into the back of another, especially if it occurs
where traffic is light and vehicles are consequently well spaced on the
road. Under these conditions, the driver’s ‘inattention’ must have been
more than just momentary.

In the US there is considerable concern about driver sleepiness, and
studies there and elsewhere have used the kinds of criteria above to deduce
the likely frequency of accidents caused by driver sleepiness. In a recent
report, entitled ‘Catastrophes, sleep and public policy’ and published in
1988 in the journal Sleep (vol 11, p 100), a group of American researchers
led by Merrill Mitler of the Scripps Clinic and Research Foundation at La
Jolla, California, concluded that of the 50 000 or so deaths from motor
vehicle accidents that occur in the US each year, 13 per cent were caused
by the driver falling asleep.

Among the studies cited by Mitler’s report is one by Peter Langlois
and colleagues from the University of Texas School of Public Health. According
to Langlois, sleepiness in drivers was the probable cause of 4994 accidents
in Texas that involved a single car, van or truck during the four-year period
1980 to 1983. Other possible factors, such as bad weather and alcohol, were
ruled out. These accidents were 10 times as likely on country roads as in
towns, presumably because such roads are more monotonous. Of particular
importance in this and other US studies is a clear influence of the time
of day: the majority of these accidents happened between 1 am and 6 am,
and there was another accident peak between 1 pm and 4 pm. The Texan study
found that the afternoon peak was particularly marked for drivers more than
46 years old.

Another American report, entitled Transportation of Hazardous Materials
and produced in 1986 by the US government’s Office of Technology Assessment,
included a detailed survey of accidents in the state of Washington involving
trucks carrying dangerous chemicals. The peak time for such accidents was
6 am. These events mostly happened under good driving conditions on a straight
road. Ironically, the authorities had first thought that it would be safest
for these trucks to drive at night, as there would be fewer other vehicles
around. They have now changed their minds.

Detailed studies from Israel and Germany also show surges of driver
sleepiness in the small hours and in the early afternoon. Sleep-related
accidents were least likely during the mid-morning and early evening; the
incidence in those periods was about one-tenth of that at 4 am. The Israeli
study, by Peretz Lavie from the Israel Institute of Technology in Haifa,
covered all car accidents in Israel over the six year period 1984 to 1989.
These investigators also found that sleep-related accidents were three times
more likely to result in serious injury or death than other road accidents.
This was because sleepy drivers did not brake to try and prevent the accident,
so the impact was worse. We have no comparable information for Britain,
but the Israeli findings suggest that if we were to look at motorway accidents
involving serious injury or death, then driver sleepiness might figure prominently.

The Sleep Research Laboratory at Loughborough has been collaborating
with the Leicestershire police in a pilot study on sleepiness among people
driving on Midlands motorways. Throughout August 1991, police officers interviewed
drivers who had been involved in what appeared to be sleep-related accidents,
such as running off the motorway or into the back of another vehicle. Drivers
of vehicles seen to be drifting across motorway lanes or who were asleep
while parked on the hard shoulder were also interviewed. Whenever possible,
the officer asked the driver a series of structured questions and completed
a standard form. The questions asked included the number of hours since
the driver last slept, the length and quality of that sleep, the time since
the journey began, time since last break from driving, the distance driven,
and whether the driver was on shift work. Drivers who were found to have
more than the legal limit of alcohol when breathalysed were excluded from
the survey. This type of survey has major limitations, as the interviewing
conditions were usually rather fraught, and interviewers and interviewees
tended to view one another with some suspicion. Nevertheless, there were
some interesting findings.

We found that among the 58 apparently sleep-related accidents and incidents
that were reported, many were clustered in three periods of the day: midnight
to 2 am, 4 am to 6 am, and 2 pm to 4 pm, with the 4 am to 6 am period the
most dangerous. Sleepy drivers detected in the early afternoon were likely
to have had irregular sleep because of shift work, for example, and to be
over the age of 45. Sleep-related accidents were least likely to happen
from 10 am to noon and 8 pm to 10 pm. Put differently, someone driving between
4 am and 6 am was 13 times as likely to have a sleep-related accident as
someone who is on the road between 10 am and noon or 8 to 10 pm.

About 11 per cent of all motorway accidents in Britain occur between
4 am and 6 am. On the face of it this is only marginally above the 8 per
cent that would be expected in any two-hour period if accidents were spread
out evenly through the day. But traffic density between 4 am and 6 am is
about one-fifth the average daily level, and when this is taken into account,
the incidence of accidents at this time is about seven times as great as
it is for other times of the day.

We found that drivers in sleep-related accidents between midnight and
2 am tended to be having a late night and were driving beyond their bedtime.
Those having accidents between 4 and 6 am had often got up very early; they
had not necessarily been driving all night. Nevertheless, we found that
the time elapsed since the driver last slept was an influential factor.
For example, the greatest incidence of sleep-related accidents occurred
when the driver had been awake more than eighteen hours. When the time of
day was excluded, the total time actually spent driving seemed not to be
so crucial unless the person had been driving for over ten hours. A quarter
of these accidents and incidents occurred within one hour of the start of
the journey, and some within 20 minutes, particularly in the small hours.

Our pilot study was a limited one, and the samples used were small.
Nevertheless, it is interesting that our findings support those from the
US and other countries that sleepiness is an important cause of motorway
accidents, though more research needs to be done. Meanwhile, the issue is
further complicated by recent claims concerning a poorly substantiated phenomenon
often dubbed ‘highway hypnosis’, and otherwise known as ‘driving without
awareness’ (DWA). While I believe this is probably no more than sleepiness
by another name, some researchers argue that it is a profound trance-like
state induced by the monotony of motorways, which can render drivers oblivious
to external events. They then become capable of running at full speed, without
braking, into the back of a stationary vehicle that has been clearly visible
for many seconds beforehand. Such an accident happened recently, and at
the ensuing trial at Worcester Crown Court in September this year, the jury
acquitted the driver of reckless driving and accepted his claim that DWA
was the cause.

Of course, drivers frequently daydream while driving along motorways
and often go into ‘trances’. But they are still aware of what is going on
around them and are not rendered incapable of responding to danger. The
alarming experience of having driven for several miles, with absolutely
no recollection of that part of the journey, is commonplace. This, however,
is not a case of DWA or of impaired driving. It merely indicates that the
driver had something more absorbing on his or her mind at the time, and
the brain had not bothered to memorise the boring part of the journey.

Whether a fatal accident is due to DWA or to sleepiness may seem a mere
academic point, but at the moment it is crucial in English law. Sleep does
not come as a bolt out of the blue; it follows a period of increasing sleepiness,
of which one is aware, and sleepy drivers must know that their driving is
impaired. A driver who has an accident after falling asleep may therefore
face the serious charge of ‘reckless driving’ (which will be substituted
by ‘dangerous driving’ in the revised Road Traffic Act, to be implemented
early this year). Causing death by reckless or dangerous driving are offenses
that can carry a prison sentence. However, drivers who go into a hypnotic-like
state quite beyond their control, of which they are totally unaware and
which is due entirely to the external circumstances of the motorway, can
claim to have been in a state of (sane) ‘automatism’. If a court accepts
this then the driver will be acquitted as he or she is seen not to be responsible
for the accident. In legal terms, mens rea (a guilty mind) cannot be established.
DWA has been claimed to be such an automatism.

In the countries where driver sleepiness has been studied in a more
systematic way than Britain, little or no mention is made of DWA or of ‘highway
hypnosis’. Nowhere in the US, Israeli and German studies of vehicle accidents
was DWA thought to be to blame; what was implicated was sleepiness. In Britain,
there is an urgent need for research to discover whether DWA really exists
– and if not, to lay it firmly to rest. In none of the incidents and accidents
encountered in our own small study can it be said that DWA was to blame.
It was plain that our drivers had been falling asleep, and most of them
realised this.

What happens when you are falling asleep? As sleepiness increases, a
glazed look comes over the eyes, visual awareness declines and ‘eye-rolling’
begins. The eyes roll up under the slowly closing eyelids, which then slowly
open and the eyes roll back down again. One complete eye-roll lasts about
two seconds, and is usually followed immediately by another. Such events
are called ‘microsleeps’, where consciousness is clouding and the brain
is losing contact with reality. It is possible to snap out of this state
for a while. Drivers can open the car windows, turn up the radio and sing
a song in the hope that all this stimulation will overcome the sleepiness.
But anyone who is really sleepy, such countermeasures are seldom effective
for more than a few minutes. Microsleeps and eye-rolling reappear, maybe
lasting for many seconds, interspersed with short bursts of greater alertness.
Successive microsleeps get longer until true sleep sets in and the head
lolls forwards, causing, with luck, a startled awakening.

A driver having microsleeps is still vaguely aware of the road but is
likely to misperceive events ahead. Limited driving skills can be maintained
to keep the vehicle on a fairly straight course or carry out simple steering
manoeuvres. Nevertheless, the vehicle may begin to drift sideways and foot-pressure
on the accelerator may relax, causing the vehicle to slow down. The driver
may still seem to be in control, but as microsleeps particularly impair
vision the immediate danger is one of collision or running off the road.
Sleepy drivers tend to drive more slowly, anyway, and try to keep in the
slow lane. When the vehicle drifts sideways the main risk is collision with
a stationary vehicle on the hard shoulder.

It is known that the brain’s 24-hour clock is set to bring sleep twice
a day: at night, and in the early afternoon. The early afternoon is therefore
a time that can produce a marked feeling of sleepiness, and this is not
due to eating lunch. This is the period when sleep-related accidents reach
their day-time peak. Many cultures, especially in hot countries, have bowed
to the inevitable and adopted the siesta as a way of life. The time of greatest
alertness, on the other hand, is in the early evening. Alcohol interacts
with this daily rhythm to worsen afternoon sleepiness, which is why many
people find that even two units of alcohol (equivalent to a pint of beer)
at lunchtime have a strongly soporific effect. While this alcohol intake
is unlikely to push drivers over the legal limit, we found in a study at
Loughborough that at this time of day it clearly impaired simulated motorway
driving. The same alcohol intake in the early evening has the same effect
on blood alcohol level but can go almost unnoticed, and driving will be
less affected. This suggests there is a strong case for setting a lower
legal blood alcohol limit for the early afternoon compared with that for
the early evening. The more sleepy drivers are feeling, the more alcohol
affects them. Tranquillisers can also be soporific, especially at the vulnerable
times of the day. Little is known about whether they present a problem for
monotonous driving, although many sleep researchers believe they do.

A large number of sleep-related accidents involve lorry drivers even
though the number of hours they can drive each day is limited by law and
is monitored by the lorry’s tachometer. But the law takes no account of
the hours the driver has been awake or the time of day. The following situation
is typical, but fortunately the end result is not: A driver gets up at 5
am, arrives at the depot at 6 am, spends four hours or so helping to load
and prepare his lorry, drives for four hours and has his minimum 45-minute
break (which he legally must do). He drives three more hours, delivers his
load, has a tea-break and waits around for two hours while his lorry is
reloaded. It is now 8 pm, and although he has driven for seven hours so
far, he is allowed by law to drive for another two hours. But he is weary
and only drives for another hour. He pulls into a service area, has a meal,
a game of cards with other drivers, and eventually gets to sleep in the
bunk at the back of the cab at midnight. He is woken up at 5 am by the general
commotion of other lorries setting off early, and while he has had only
five hours sleep, he has had his legal minimum of eight hours rest. So he
decides to set off as well, with the aim of getting back to base, off work
and home by lunch-time. He falls asleep at the wheel at 5.30 am and hits
the central barrier. Few radio listeners hearing the motoring news-flash
about the accident and the resultant motorway blockage realise why so many
of these announcements occur at this time of day.

One long-distance lorry driver recently gave me the following verbatim
account: ‘Almost every day I come across lorry drivers who tell stories
of falling asleep at the wheel. Today one told me he stopped at traffic
lights and fell asleep. He woke up with the lights on green and horns blowing.
Many times early in the morning lorries can be seen wandering on the motorway,
the driver falling asleep, trying to make a service area to collapse over
the wheel. The problem is very grave and dangerous, and I believe is causing
accidents and deaths.’ This driver believes the authorities are indifferent
to the problem, even though the nine hours driving time allowed by the law
is longer than the average working day and total working-hours are almost
open-ended. He blames the employers too: ‘Many transport companies work
their drivers the full hours. Many drivers live entirely in their cabs.’
Some data on sleepiness among these professional drivers has been collected,
though not nearly enough. Even less is known about other vulnerable groups,
such as taxi drivers working nights.

Some drivers face the additional problem of severely disturbed sleep,
which causes profound daytime sleepiness even if the sleep seems to be of
a reasonable length. The commonest disorder of this type is a form of impaired
breathing called ‘sleep apnoea’ (‘Warning: snoring can damage your health’,
¿ìè¶ÌÊÓƵ, 12 December 1985), which is typically a collapse of the throat
that gags the sleeper and causes them to awaken momentarily. This may happen
many times a night, but the sleeper is usually oblivious to it even though
there is very severe snoring. Obesity makes matters worse as the weight
of the fat in the neck further compresses the sleeper’s throat. Long-distance
lorry drivers seem particularly vulnerable to this problem as, according
to John Stradling of the Churchill Hospital in Oxford, many of them are
obese (‘Obstructive sleep apnoea and driving’, British Medical Journal,
vol 298, p 905). Stradling quotes three separate studies from the US which
show people who suffer from sleep apnoea are seven times as likely as those
who sleep normally to have a road accident. In most cases the disorder can
be cured.

In Britain, we need to do more research to discover the real extent
of sleepiness in drivers. Our pilot project and research done abroad suggest
that it is a major problem requiring more public awareness, further road
safety measures, and maybe legislation both with regard to alcohol limits
and to the working, rather than driving, hours of professional drivers.

Meanwhile, drivers who find themselves feeling sleepy, especially in
the early morning, should adopt a simple solution, which is to get off the
motorway, stop driving and get at least some sleep. Trying to wake yourself
up with a brisk walk round the service area, drinking lots of coffee, or
playing video games in the foyer are only of short-term benefit in the small
hours, though these devices may work better in overcoming the shorter, early
afternoon trough of sleepiness. Breaks from driving may be helpful in relieving
sleepiness, but if they are long and taken at, say, 11 pm, they may be counterproductive
if this pushes the ensuing driving into the vulnerable hours.

Jim Horne is professor of psychophysiology at the Loughborough University
of Technology and Director of the university’s Sleep Research Laboratory.
He is author of Why We Sleep, Oxford University Press (1989), £12
(pbk).

Acknowledgement: The considerable help of Inspector Fred Rankin, of
the motorway patrol headquarters of Leicestershire Constabulary, is gratefully
acknowledged, as is the cooperation of the other police forces in the Midlands
Motorway Thematic Policing Group.