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22 novembre 2015
Accident Analysis and Prevention
2015;85:22-29
Examining signs of driver sleepiness,
usage of sleepiness countermeasures
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

Chat-logomini

ERGOLOGY
 
abstract
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.