and the
associations with sleepy driving
behaviours
and
individual factors
Christopher N. Watling, Kerry A. Armstrong,
Igor Radunb
Centre for Accident Research
and Road Safety - Queensland, Institute of
Health and Biomedical Innovation, Queensland
University of Technology, Australia b Stress
Research Institute, Stockholm University,
Sweden
The impairing effect from sleepiness is a
major contributor to road crashes. The ability
of a sleepy driver to perceive their level of
sleepiness is an important consideration for
road safety as well as the type of sleepiness
countermeasure used by drivers as some
sleepiness countermeasures are more effective
than others. The aims of the current study were
to determine the extent that the signs of driver
sleepiness were associated with sleepy driving
behaviours, as well as determining which
individual factors (demographic, work, driving,
and sleep-related factors) were associated with
using a roadside or in-vehicle sleepiness
countermeasure. A sample of 1518 Australian
drivers from the Australian State of New South
Wales and the neighbouring Australian Capital
Territory took part in the study. The
participants' experiences with the signs of
sleepiness were reasonably extensive. A number
of the early signs of sleepiness (e.g., yawning,
frequent eye blinks) were related with
continuing to drive while sleepy, with the more
advanced signs of sleepiness (e.g., difficulty
keeping eyes open, dreamlike state of
consciousness) associated with having a
sleep-related close call. The individual factors
associated with using a roadside sleepiness
countermea- sure included age (being older),
education (tertiary level), difficulties getting
to sleep, not continuing to drive while sleepy,
and having experienced many signs of sleepiness.
The results suggest that these par- ticipants
have a reasonable awareness and experience with
the signs of driver sleepiness. Factors related
to previous experiences with sleepiness were
associated with implementing a roadside
countermeasure. Nonetheless, the high
proportions of drivers performing sleepy driving
behaviours suggest that concerted efforts are
needed with road safety campaigns regarding the
dangers of driving while sleepy.
Signs of sleepiness Sleepiness
countermeasures Individual factors Australian
drivers
1. Introduction
Driver sleepiness is a substantial
contributor to road crashes. Current estimates
suggest that the effect from sleepiness accounts
for 20% of all fatal and severe crashes (Connor
et al., 2002; Kecklund et al., 2012; Nabi et
al., 2006). However, without an objective
measure of a driver's level of sleepiness, such
as breath alcohol content level as with drink
driving, the exact incident levels are suggested
to be greater than current estimates (Cercarelli
and Haworth, 2002). Many crashes are
multifactorial in nature and it is likely that
sleepiness could have contributed to crashes
ascribed to other risky driving behaviours
(Watling et al., 2013). Reducing the occurrence
of driving while sleepy in the general driving
population is largely reliant on educational
campaigns that publicise the risks associated
with driving while sleepy. Therefore, mitigating
the risk from sleepiness is largely reliant on
drivers' awareness of the signs of sleepiness
and their subsequent actions they take to
counteract their sleepiness.
1.1. Experiencing signs of
sleepiness
The ability of a sleepy driver to perceive
their level of sleepiness is an important
consideration for road safety. Simulated driving
studies reveal a good correspondence between a
driver's awareness of sleepiness and their
likelihood of falling asleep (Horne and Baulk,
2004; Reyner and Horne, 1998b; Williamson et
al., 2014). More- over, drivers who rate
themselves at a high levels of sleepiness and at
a high likelihood of falling asleep also have
impaired driving performance levels with more
centreline crossings and crashes during
simulated driving (Williamson et al., 2014).
Other driver simulator studies reveal good
correspondence between drivers' subjective and
physiological sleepiness, as well as greater
frequency of line crossings when subjective and
physiological sleepiness is high (Horne and
Baulk, 2004; Reyner and Horne, 1998b).
Considered together, these results suggest that
drivers have some level of insight of their
level of sleepiness and high levels of
subjective sleepiness corresponds with impaired
driving performance.
The insight of individuals regarding their
ability to recognise particular signs of
sleepiness has been explored. For instance,
Kaplan et al. (2007) examined the associations
between experiencing certain signs of sleepiness
with the ability to predict sleep onset with a
computerised task. The results suggest
individuals were aware of their sleepiness and
could report experiencing particular signs of
sleepiness, as sleepiness levels increased the
amount of signs of sleepiness experienced also
increased. A study by Howard et al. (2014)
examined the relationships with particular signs
of sleepiness and the corresponding
physiological, subjective, and performance
indices during a simulated driving task. As
physiological and subjective sleepiness
increased and driving performance subsequently
became more impaired, the frequency with which
the signs of sleepiness were reported increased
correspondingly. Signs of sleepiness that were
specifically associated with severely impaired
simulated driving performance were related to
visual disturbances (e.g., struggling to keep
your eyes open) and overt signs of sleepiness
impaired driving performance (e.g., difficulty
keeping to middle of road). These studies of
specific signs of sleepiness similarly suggest
that drivers have some level of insight into
their level of sleepiness and are able to report
specific signs of sleepiness.
1.2. Usage of sleepiness
countermeasures
When a driver becomes aware of experiencing
certain signs of sleepiness, the individual can
choose to implement a sleepiness countermeasure.
A number of sleepiness countermeasures are
available to the driver. These sleepiness
countermeasures can be grouped broadly into
categories based on where they are imple-
mented, being at the roadside or in-vehicle.
When implementing a roadside sleepiness
countermeasure, the driver must first cease
driving by pulling their vehicle over to the
roadside, this action automatically eliminates
the possibility of the driver falling asleep
while driving.
Roadside sleepiness countermeasures include:
stopping and taking a rest break (which could
also include eating and or having a drink (e.g.,
coffee), 'stretching' ones legs, amongst other
activ- ities), stopping and napping, or swapping
drivers. Experimental studies suggest that
napping and consuming caffeine are the most
effective countermeasures for reducing
physiological and subjec- tive sleepiness (De
Valck and Cluydts, 2001; Horne and Reyner, 1996;
Watling et al., 2014b). Direct comparisons of
napping and caffeine suggest caffeine produces
the most consistent effects (Horne and Reyner,
1996); this is likely due to ease of
administering caffeine versus the obvious
difficulty of napping on cue. Rest breaks are a
commonly employed roadside countermeasure (Anund
et al., 2008); although, experimental studies
suggest the effectiveness of rest breaks are
short lived when compared to nap breaks (Watling
et al., 2014b). Swapping drivers is a commonly
promoted counter-measure although its
effectiveness in relation to the other roadside
countermeasures is unknown. Last, Cummings et
al. (2001) demonstrated drivers who used a
highway rest break area had a lower relative
risk of being involved in a crash along a rural
interstate highway.
In-vehicle sleepiness countermeasures are
actions the driver initiates while driving to
increase their level of arousal. These can
include listening to music and opening the
window or turning on the air conditioner.
Overall, experimental studies suggest the
effectiveness of in-vehicle countermeasures is
relatively low.
For instance, listening to music has a small
effect for reducing subjective sleepiness, with
a less pronounced effect for reducing
physiological sleepiness (Reyner and Horne,
1998a; Schwarz et al., 2012). Similarly, opening
the window/turning on the air conditioner has a
small, albeit, transient effect on subjective
sleepiness; however, the effect on physiological
sleepiness is negligible to non- existent
(Reyner and Horne, 1998a; Schwarz et al., 2012).
Overall, in-vehicle countermeasures have limited
effectiveness for reducing sleepiness. However,
these two in-vehicle countermeasures are popular
with drivers and are utilised more so than the
more effective roadside sleepiness
countermeasures (Anund et al., 2008; Armstrong
et al., 2010; Nordbakke and Sagberg, 2007).
It is possible that a number of demographic,
work, driving, and sleep-related factors could
influence an individual's use of a sleepiness
countermeasure. Demographic factors such as age
(being younger) and sex (being male) have been
previously related to driving while sleepy,
employing rest breaks (Phillips and Sagberg,
2013; Radun et al., 2015; Watling, 2014), and
having a sleep-related crash (Åkerstedt
and Kecklund, 2001). Work related factors might
influence the choice of sleepiness
countermeasure as shift workers and professional
drivers have greater experience with sleepiness
and driving (Anund et al., 2008; Di Milia, 2006)
and this could predispose them to utilise the
more effective roadside countermeasures.
Another set of factors that could influence
the choice of a sleepiness countermeasure could
be the individual's previous experiences with
driving while sleepy. That is, previous
experiences with having a sleep-related close
call or crash might lead an individual to use
roadside sleepiness countermeasures as they are
more effective. Additionally, survey studies
suggest drivers also perceive roadside
countermeasures as effective sleepiness coun-
termeasures (Anund et al., 2008; Armstrong et
al., 2010). Sleep health related factors might
also influence an individual's choice of
sleepiness countermeasure. Individuals that
experience frequent daytime sleepiness or have
poor sleep quality are likely to suffer from
excessive daytime sleepiness (Bartlett et al.,
2008) and might be inclined to utilise the more
effective roadside sleepiness
countermeasures.
The utility of outcomes derived from
laboratory and simulator studies restricts the
generalisation of these studies to the general
driving population. Specifically, it is unknown
what proportions of Australian drivers have
previously experienced specific signs of
sleepiness and the associations between specific
signs of sleepiness and sleepy driving
behaviours are also unknown. The usage of the
various countermeasures has yet to be quantified
in a large sample of Australian drivers and
identifying factors associated with implementing
a roadside or in-vehicle countermeasure needs to
be performed on a large sample of Australian
drivers. Understanding the associations with the
signs of sleepiness and countermeasure usage
with driving behaviours and individual factors
could be important information for road safety
educational campaigns. The first aim was to
examine the proportion of drivers who have
previously experienced the signs of sleepiness
and how these signs of sleepiness were
associated with the two sleepy driving
behaviours of continuing to drive while sleepy
and having a sleep-related close call. The
second research aim sought to identify the
sleepiness countermeasures that are used by
drivers and what individual factors were
associated with using a roadside or in-vehicle
sleepiness countermeasure.
4. Discussion
Overall, this study has shown that a
concerning proportion of drivers (69.83%) have
continued to drive while sleepy in the last five
years. Driving while experiencing acute
sleepiness is a known risk factor for having a
sleep-related crash (Connor et al., 2002;
Kecklund et al., 2012) as sleepiness can impair
a number of psy- chological processes that are
needed to safely control a vehicle (e.g.,
Åkerstedt et al., 2005; Campagne et al.,
2004; Jackson et al., 2012; Killgore et al.,
2006). Moreover, in the last five years 16.73%
of drivers reported having a sleep-related close
call, with 2.44% reported having a sleep-related
crash. These proportions suggest that the
drivers in this sample have a reasonable amount
of expe- rience with sleepy driving.
The first aim sought to examine the
proportion of drivers who have previously
experienced signs of sleepiness while driving
and how these signs of sleepiness were
associated with sleepy driving behaviours. The
most common signs of sleepiness experienced by
over half of the participants were yawning,
changing position fre- quently, frequent eye
blinks, and difficulty concentrating on driving.
Driver sleepiness simulator studies have shown
that these early signs of sleepiness (e.g.,
yawning, postural changes, and frequent eye
blinks) are common while experiencing low levels
of sleepiness (Howard et al., 2014; Nordbakke
and Sagberg, 2007; Rogé et al., 2001;
Sagberg et al., 2004). Moreover, yawning,
frequent eye blinks, and difficulty
concentrating on driving were also significantly
associated with continuing to drive while sleepy
at the multivariate level after controlling for
age and sex. The least experienced signs of
sleepin1ess were difficulty keeping eyes open
and dreamlike state of consciousness, which are
presumably signs of sleepiness that are
experienced when extremely sleepy (Ogilvie and
Wilkinson, 1984).
At the multivariate level, three signs of
sleepiness were associated with having a
sleep-related close call. These were, difficulty
keeping eyes open, difficulty concentrating on
driving, and dream-like state of consciousness.
Difficulty keeping eyes open was the sign of
sleepiness with the largest relationship with
having a sleep related close call, followed by
dreamlike state of consciousness, and difficulty
concentrating on driving. Support for the
current findings is found with driving simulator
studies, which have also shown that difficulty
keeping the eyes open has a strong relationship
with variation of lateral positioning (Howard et
al., 2014; Sagberg et al., 2004) and is a sign
of sleepiness often experienced just prior to
falling asleep while driving (Nordbakke and
Sagberg, 2007). Consequently, when an individual
is having difficulty keeping their eyes open,
alpha and theta intrusions are apparent in the
waking EEG (Åkerstedt and Gillberg, 1990;
Gillberg et al., 1994). It has been suggested
that some drivers consider signs of sleepiness
as trivial (Dinges, 1995) and or may fail to
appreciate the seriousness of some signs of
sleepiness (Horne and Reyner, 2001). Considered
together, the current findings reinforce that
concerted efforts are still needed with road
safety campaigns regarding the dangers of
driving while sleepy.
The second aim of the current study was to
examine the usage of roadside or in-vehicle
sleepiness countermeasures. Overall, the three
most commonly used countermeasures were turning
up/on the radio/stereo, followed by opening the
window, and stopping the vehicle and getting out
of the car. These prevalence rates are somewhat
concerning, as two of the three most commonly
used countermeasures were the least effective
countermeasures for reducing sleepiness (e.g.,
Reyner and Horne, 1998a; Schwarz et al., 2012).
Nonetheless, the finding that drivers use the
least effective sleepiness countermeasures is
consistent with previous research (Anund et al.,
2008; Vanlaar et al., 2008).
The more effective countermeasures of
napping and consuming caffeine (e.g., De Valck
and Cluydts, 2001; Horne and Reyner, 1996;
Watling et al., 2014a,b) were only used by 9.29%
and 8.30% of participants respectively.
International (e.g., Anund et al., 2008;
Nordbakke and Sagberg, 2007) and Australian
driver surveys (e.g., Armstrong et al., 2010)
reveal napping and caffeine are considered by
most drivers as a highly effective sleepiness
countermeasure. It is a concern that the use of
napping and caffeine in the Australian sample is
much lower than what has been reported in a
Swedish (napping: 18.00%, caffeine: 45.00%:
Anund et al., 2008), Norwegian (napping: 10.00%,
caffeine: 15.00%: Nordbakke and Sagberg, 2007),
and Canadian (napping: 14.80%, caffeine: 29.50%:
Vanlaar et al., 2008) samples. Some of the
differences with the use of caffeine as a
sleepiness countermeasure could be explained by
the per capita consumption (kg) of coffee, being
7.14 for Sweden, 9.51 for Norway, and 6.22 for
Canada versus 3.73 for Australia (International
Coffee Organization, 2011). However, the
differences in napping use between Sweden,
Canada and Australia are not so easily
explained. These outcomes suggest that other
factors may be associated with use of certain
sleepiness countermeasures other than how
effective the countermeasure is regarded.
Several of the variables that were
associated with drivers' use of a roadside or
in-vehicle sleepiness countermeasure appear to
be experience based. Age (being older) and being
a professional driver were associated with
implementing a roadside sleepiness
countermeasure. Several studies have shown that
older drivers are more likely to stop driving
and employ the more effective sleepiness
countermeasures such as a napping or rest breaks
(Anund et al., 2008; Nordbakke and Sagberg,
2007; Watling, 2014) and the current results are
consistent with previous research. In contrast,
younger drivers are more likely to engage in
various types of risky driving (Begg and
Langley, 2001; Hatfield and Fernandes, 2009)
including driving while sleepy (Phillips and
Sagberg, 2013; Radun et al., 2015; Watling,
2014). It is likely that professional drivers
have more on-road experience with sleepiness and
thus use the more effective roadside sleepiness
countermeasures (e.g., Asaoka et al.,
2012).
A notable finding from the current study was
that having experienced more of the signs of
sleepiness was related to use of a roadside
countermeasure. This result is an encouraging
result for road safety, as it suggests that a
proportion of drivers can self-regulate their
sleepiness by ceasing driving after perceiving
their heightened level of sleepiness and employ
a roadside sleepiness countermeasure. Likewise
self-reported difficulties getting to sleep were
also associated with using a roadside sleepiness
countermeasure. Individuals reporting sleeping
difficulties are likely more cognizant of the
impairing effect that sleepiness can have on
neurobehavioural functioning (Philip and
Åkerstedt, 2006) and in the context of the
current study are seemingly more proactive with
implementing a roadside sleepiness
countermeasure.
The potential reasons that some drivers use
in-vehicle counter- measures are also worth
discussing. Implementing an in-vehicle
sleepiness countermeasure allows the driver to
continue their journey without stopping. In the
current study, drivers who had continued to
drive while sleepy in the last five years were
associ- ated with employing in-vehicle
countermeasures. As such, notions of motivations
to arrive at ones destination (Watling et al.,
2014a) and time urgency (Fernandes et al., 2010)
could facilitate implementing an in-vehicle
sleepiness countermeasure. Surprisingly, survey
data suggests that drivers are cognizant that
in-vehicle sleepiness countermeasures are not as
effective as roadside countermeasures (Armstrong
et al., 2010; Nordbakke and Sagberg, 2007). It
is also likely that risk perception of the
dangerousness of sleepy driving could also be a
contributing factor for wanting to employ the
less effective, in-vehicle sleepiness
countermea- sure while continuing to drive. It
must be noted that turning up/on the
radio/stereo was the most commonly reported
sleepi- ness countermeasure used by
participants. Therefore, attitudinal and
behavioural change is likely necessary regarding
some drivers'choice of implementing an
in-vehicle countermeasure to reduce their
sleepiness.
The results of the current study need to be
considered in light of its limitations. First,
and foremost, the data was collected via
self-reported methods and thus issues from
recall and social desir- ability bias are a
possibility. Additionally, given the
retrospective and cross-sectional nature of the
study design, causality of the obtained
relationships cannot be inferred. It should also
be noted that drivers aged of 22 years or less
(23.21%) would not have five years of driving
experience to draw upon and this lack of experi-
ence could have influenced their responses to
the questionnaire. The roadside countermeasure
logistic regression model accounted for a small
amount of the variance and therefore, other
factors such as motivations to continue driving
and reaching ones destination could possibly
account for a driver's utilisation of sleepiness
countermeasures. Future research could seek to
improve upon the current study limitations. For
instance, longitudinal studies concerning use of
sleepiness countermeasures and sleepy driving
behaviours are lacking. More importantly, the
effects of general driving experiences as well
as the frequency of experiencing sleepy driving
incidents, the driver's motivations to drive
sleepy, and the usage of countermeasures is
scantly understood and needs to be further
explored to better understand the prevalence of
sleepy driving instances.
In conclusion, the present study suggests
that many drivers are aware of the signs of
sleepiness and they have experienced them
previously. To the authors' best knowledge, this
is the first Australian study that has
quantified what signs of sleepiness drivers have
previously experienced and what sleepiness
countermeasures are being used by a large sample
of drivers and thus, the infor- mation detailed
in this study is of benefit to road safety
agencies. Many of these signs of sleepiness were
associated with the sleepy driving behaviours of
continuing to drive while sleepy and having a
sleep-related close call. The current study also
found the most commonly used sleepiness
countermeasures were turning on the
radio/stereo, opening the window, and stopping
the vehicle and getting out of the car.
Moreover, a number of individual factors were
associated with using a roadside sleepiness
countermeasure. These factors included age
(being older), education (tertiary level),
difficulties getting to sleep, not continuing to
drive while sleepy, and having experienced many
signs of sleepiness. No individual is immune to
the effect of sleepiness while driving and
increasing the usage of the more effective
roadside sleepiness countermeasures could lead
to improvements in road safety outcomes and
provide a safer road environment for all
drivers.
