Factors associated with different levels of daytime sleepiness among Korean construction drivers: a cross-sectional study

Occupational health and safety is a major concern worldwide. The World Health Organization (WHO) emphasizes the importance of improving workers’ health and reducing work-related injuries [1]. Most countries have formulated policies consistent with global regulations to enhance the safety and health of workers [1‐3]. Previous studies have examined integrated occupational safety and health management for employees, such as safety education, stress management, and health promotion programs [4, 5]. However, occupational drivers are still vulnerable to work-related injuries and health issues, especially sleep related problems because insomnia is also important in predicting injuries [6]. According to the Emergency Department of the University Hospital data, specific sleep related problems such as poor sleep quality, short sleep duration, and excessive daytime sleepiness are common causes of an increase in work-related injury risks [7]. For example, sleep deprivation, sleepiness and poor sleep quality was independently associated road accident among truck drivers with obstructive sleep apnea [8]. Occupational drivers’ sleep health components are uniquely related to not only occupational accidents but also individual health concerns, such as cardiovascular disease [9‐13]. Therefore, occupational health care providers must understand the health vulnerability of occupational drivers and develop relevant health management programs.

Commercial vehicle accidents are the leading cause of occupational fatalities, and can be a huge economic burden on the concerned employers and industry. The Industrial Accident Prevention and Compensation Policy Bureau [14] reported that approximately half of occupational drivers are injured in vehicle accidents, which accounts for nearly half of the occupational accidents in Korea. Furthermore, the US National Institute of Occupational Safety & Health (NIOSH) [3] stated that 22,000 workers died in work-related vehicle accidents from 2003 to 2014 and that the United States (US) employers spent about US $25 billion on work-related motor vehicle crashes in 2013; US $65,000 per nonfatal injury and US $671,000 per death. Regarding the vehicle type, in Korea, construction-related vehicles are ranked second (n = 4.44 per 1.0 million registered vehicles) in terms of their involvement in fatal crashes [11]. Therefore, it is imperative to understand traffic accident characteristics and relevant risk factors among occupational drivers to reduce motor vehicle mortality.

In previous studies, an increased risk of traffic accidents is associated with excessive fatigue, other health problems as well as poor sleep, such as insomnia [9, 15‐17]. For example, occupational drivers in the transportation industry have reported poor sleep quality on working days [17], a higher rate of chronic diseases or obesity than the adult working population [18], high levels of job stress [19], underdiagnoses of obstructive sleep apnea syndrome [20] and more depressive symptoms [21]. Several studies have reported drowsy driving as a major risk factor for motor vehicle accidents [9‐11], the mortality for which is high in drivers of commercial trucks and construction-related vehicles [11]. Drowsy driving was reported to be one of the major causes (22.5%) of traffic accidents in Korea and can be considered equally harmful as drunk driving [22]. In addition, driving fatigue and daytime sleepiness are critical predictors of drowsy driving by occupational drivers [16, 23], and increase driving risks among them [9, 16, 24, 25]. Fatigue is a comprehensive indicator that reflects physical exertion, emotional distress, and physiological impairment [26]. Daytime sleepiness influences poor health and occupational risk as a core component [27], a predisposing factor [28], and a co-occurring condition [29].

Few studies have examined the different levels of daytime sleepiness in occupational drivers [9, 16] or vehicle accident victims compared to the general adult population [24, 29‐31]. These studies have frequently used the Epworth Sleepiness Scale (ESS) to evaluate daytime sleepiness propensity of individuals or certain occupation groups [9, 16, 24, 32, 33]. The ESS divides the severity of daytime sleepiness into “mild (or normal),” “moderate,” and “severe” levels [32, 34, 35]. Previous studies examined the association between daytime sleepiness and motor vehicle accidents or injuries using ESS scores [24] or severity classification [16, 30]. To effectively prevent underreporting of drowsy driving accidents, multiple levels of drowsiness behind the wheel have been discussed in previous literature [36]. Some studies have reported an inverse U-shaped severity of ESS and driver injury [32]; thus, a simple summation of ESS score as a linear pattern may not reflect this phenomenon accurately.

Previous studies have examined construction drivers’ physical and emotional health concerns, such as driving fatigue, mood disorders (including depression), stress, sleep deprivation, and bodily pain [16, 17, 26]. However, few have focused on the daytime sleepiness, traffic accidents, and health conditions, particularly of construction drivers because of several reasons. First, most studies have focused on individual characteristics rather than occupational or institutional factors. Current policies emphasize that occupational safety and health promotion should consider not only individual characteristics but also organizational support; thus, a broader range of risk factors should be evaluated. Second, homogenous groups among diverse occupation types should assess the unique characteristics of each occupation [16, 29]. Third, both driving fatigue and daytime sleepiness must be included when studying this topic, as they are interrelated and could influence the occupational drivers’ health and safety. Thus, it is necessary to conduct a more comprehensive assessment of sociodemographic, health-related, and occupational characteristics when focusing on this vulnerable group.

The current study sought to examine the individual and occupational factors related to daytime sleepiness levels and identified their association with the driving risk of commercial drivers working at construction sites. Several occupational and health-related factors were significantly associated with higher levels of daytime sleepiness among the construction drivers, including driving fatigue. Approximately 40% of construction drivers had at least “moderate” levels of daytime sleepiness.

Higher levels of driving fatigue were related to “moderate” and “severe” daytime sleepiness. In this study, driving fatigue was highest in the “severe” daytime sleepiness group, followed by the “moderate” daytime sleepiness group and “mild” daytime sleepiness group. There is supporting evidence of a strong association between daytime sleepiness and fatigue, which play significant roles in exacerbating the occurrence of car crashes similar to the previous studies [9, 10, 16, 24, 25]. The US Department of Transportation established the National Highway Traffic Safety Administration (NHTSA) strategic plan to control fatigue and daytime sleepiness and ensure driver safety by implementation of specific features, such as vehicle warning systems and roadway rumble strips [51]. Occupational healthcare providers should offer comprehensive health promotion programs, such as advising about healthy sleep habits and work schedules, and employers should make an effort to reduce excessive fatigue at work, by preventing long working hours or irregular work schedules as recommended [33]. For example, in Korea, there are approximately 300 rest areas built 25 km apart and the government plans to construct additional service areas for resting on the expressways and national highways [52]. The government also needs to provide regular medical checkups for construction drivers, with sleep problems, that threaten their safety while driving.

Interestingly, participants who had experienced more depressive symptoms in the past 12 months were less likely to experience “moderate” daytime sleepiness, but this was not found in the “mild” daytime sleepiness or “severe” daytime sleepiness groups. In general, depression is known to involve physical and emotional factors that affect daytime sleepiness as consistent to the previous literature [9, 16]. However, the multivariate regression analysis were unexpected because the relative association between depressive symptoms and daytime sleepiness becomes weaker when considering the impact of other factors. In general, the relationship between depression and sleep is bidirectional and complicated [53]. Since depression is known to result in both sleep deprivation and excessive sleep [53], the effect of depression on daytime sleepiness may be inconsistently shown the following day.

Recent studies reported that the pathophysiological mechanisms of depression induce stable arousal during the day [54, 55], which decreases daytime sleepiness. Future studies should reconsider the choice of instruments to measure depression. The measure of depressive symptoms used in this study was developed to assess the experience of depression and is highly focused on the general public’s negative emotions [39]. However, daytime sleepiness and driving fatigue are considered more as physical symptoms [16]. Thus, it is possible that the relationship between depressive symptoms and daytime sleepiness was not clearly revealed in this study. Considering the complex nature of depression and sleep disturbances, a deeper examination of these two conditions is necessary, using different measures and by focusing on the conceptual framework of depression and other comorbidities.

In contrast, higher levels of subjective sleep quality were associated with “moderate” daytime sleepiness. It is important to consider the effect of both sleep quantity and quality on health conditions [17]. Previous studies reported that sleep quality is related more to the safety issues or occupational performance of drivers than sleep duration [17, 25]. For example, the group with poor sleep quality reported higher levels of daytime sleepiness and daytime fatigue even after having the same amount of sleep [31]. In addition, the occupational drivers’ irregular work schedules can result in poor sleep quality which is related to drowsy driving. Occupational health providers should educate occupational drivers about proper sleeping habits compensating for insufficient sleep, and allow access to medication, if necessary.

We also investigated the differences in driving characteristics among the daytime sleepiness groups. There were significant differences in the global traffic accident risk and number of near misses in the past year. The higher the level of daytime sleepiness, the higher the risk of car accidents and the higher the number of near misses. However, it was not significantly associated with traffic accidents in the past year, possibly due to the limitation of self-reporting and other biases as similarly found in the literature [56]. Daytime sleepiness is associated with car accidents that threaten the safety of drivers as consistent to the previous studies [9, 10, 15‐17, 24, 25]. Therefore, daytime sleepiness should be properly controlled through individual efforts, implementation of environmental improvement initiatives by the company, and following of public health regulations [57]. Occupational drivers are particularly vulnerable to daytime sleepiness [25]. Consequently, a medical check-up of excessive daytime sleepiness, which considers other comorbidities, such as obesity or obstructive sleep apnea [58], is highly recommended for occupational drivers.

We also found that dangerous driving activities were significantly different according to the level of daytime sleepiness. The “severe” daytime sleepiness group reported higher levels of forced driving, driving over the speed limit, and cell phone use compared to the other groups. Specifically, driving over the speed limit was a key activity that was associated more with the “severe” daytime sleepiness group and it was greater than even in the “moderate” daytime sleepiness group. These findings support previous studies that focused on the association between sleepiness and hazardous behavior, including over speeding or using a cell phone [16, 24]. Bener et al. [24] reported that drivers who had vehicle accidents were less likely to use a safety belt, comply with the regular speed limit when driving, and had higher scores of daytime sleepiness than drivers who did not have vehicle accidents. In addition, occupational drivers tend to violate regulations when they feel exhausted and drowsy while on duty [59]. Similar to a Chinese study, such illegal and hazardous driving behaviors could predispose them to injuries while driving [60]. It is very important to prevent job-related injuries, considering that almost half (48%) of the drivers who went over the speed limit wear not wearing a safety belt, while drivers who conformed with the regular speed limit account for 21% of the total number of fatal crashes in the US [61]. One of the most effective ways to prevent vehicle crashes by complying with safety regulations is to promote an altruistic attitude, foster social support from others, create safety campaigns, and provide education about traffic violations using mobile phone [36, 59, 62, 63] to prevent risky behaviors while driving.

Our findings also showed that there were significant differences in break time among the three different daytime sleepiness groups. This coincides with the findings of Chen and Xie [64] about the importance of a short break while driving. According to research on long-haul drivers, working overtime negatively affects driving-related factors, such as concentrating while driving and driving skills [17]. There is evidence that insufficient rest can cause drowsy driving as well as vehicle crashes related to drowsy driving [15]. It has also been reported that half of the occupational drivers suffer from chronic fatigue and this is associated with a short break time and excessive work-related stress [19]. In 2017, the Korean government announced the enforcement of a presidential decree to take a mandatory 30-min break after every 4 h of driving to reduce daytime sleepiness and fatigue [65]. Therefore, formulation of punitive policies is highly recommended when mandatory education for drivers is not provided. Constant surveillance should also be conducted to reduce the physical and psychological burden while driving. In addition, it is important to develop more effective interventions that could be used during a short break. For example, a recent study showed the effectiveness of a relaxation technique during naps to improve occupational performance of the drivers’ duties [66]. Therefore, occupational health providers should educate construction drivers using specific strategies or evidence-based interventions.

A significant number of construction drivers experience excessive daytime sleepiness, which is associated with health problems and occupational risk. It is important to reduce the negative impact of driving fatigue and other factors on daytime sleepiness. Our study findings suggest that occupational health care providers should pay attention to development and implementation of health management interventions to reduce driving fatigue that incorporate the drivers’ health-related characteristics. Specifically, occupational health care providers should provide integrated health promotion programs for drivers working at construction sites dealing with physical, mental, and occupational factors. Professional organizations need to establish internal regulations and public policies to promote health and safety among occupational drivers who specifically work at construction sites.