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INTRODUCTION — Drowsy driving and fall-asleep crashes are common and often result in fatalities and serious injuries because drivers fail to use maneuvers to avoid or mitigate crash severity. Teenagers as a group are at highest risk for crashes related to drowsy driving; other high-risk groups include patients with obstructive sleep apnea (OSA) and other sleep disorders, shift workers, medical house staff, law enforcement officers, and commercial drivers.
Individuals at high risk for drowsy driving crashes should be identified and educated about how to recognize symptoms of drowsy driving and about countermeasures they can institute to reduce crash risk. Education has been endorsed by a National Highway Transportation Safety Administration (NHTSA) expert panel , by the American Academy of Sleep Medicine , and by the American Thoracic Society . Additionally, sleep disorders and other medical conditions that may contribute to sleepiness while driving are important to recognize and treat.
This topic will review important aspects of the evaluation and management of drowsy driving. An approach to the evaluation of excessive daytime sleepiness more generally is presented separately. (See "Approach to the patient with excessive daytime sleepiness".)
EPIDEMIOLOGY — Drowsy driving is a very common problem. In polls conducted by the National Sleep Foundation and others, about 60 percent of drivers admit to driving while feeling sleepy, about 40 percent have nodded off or fallen asleep while driving during the prior year, and about one-quarter report drowsy driving at least once per month [4,5]. Among teenagers, 50 to 70 percent admit to drowsy driving in the past year, and 15 percent report doing so at least once per week [5,6].
Crash data from police reports and federal databases in the United States indicate that an average of 83,000 crashes occur annually because of drowsy driving, causing 1000 deaths and 71,000 injuries annually . Crashes due to drowsy driving are a particular concern in teenagers and young adults. (See 'Teenage and young adult drivers' below.)
Drowsy driving accounts for an estimated one in six fatal crashes and one in eight crashes leading to hospitalization of the driver or passengers . These high proportions are consistent with the observation that drowsy-driving crashes occur at high speed, with an absence of avoidance maneuvers such as braking or swerving that could mitigate crash severity . Off-road deviation, rear-ending another vehicle, and late-night or early-afternoon timing of a crash also increase the likelihood that a crash was related to drowsy driving .
The number of crashes due to drowsy driving may be underestimated, as drivers may be unaware of their sleepiness or reluctant to volunteer it to police. In addition, many law enforcement officers are insufficiently trained to recognize drowsy-driving crashes, and during the immediate aftermath of a crash, the driver may appear to be alert because of the sympathetic hyperactivity that accompanies the event. Sleepiness may be overlooked when alcohol is also involved.
EFFECTS OF DROWSINESS ON DRIVING — Drowsiness impairs a host of cognitive functions that are important for driving, including judgment, attention, executive function, cognitive processing speed, memory, reaction time, and muscular coordination . These cognitive effects may be compounded by "microsleeps" – brief, involuntary episodes of sleep, which can last from a fraction of a second up to 30 seconds [11-15]. (See "Insufficient sleep: Definition, epidemiology, and adverse outcomes", section on 'Effects of acute sleep deprivation'.)
During a microsleep, an individual experiences a temporary lapse in consciousness and is unable to respond to sensory stimuli. Electroencephalography (EEG) shows sleep in the theta range (4 to 7 Hz) superimposed on a background of wakefulness (alpha) rhythm (8 to 12 Hz). Despite EEG evidence of sleep, most individuals are unaware of a microsleep and believe they were awake. Behavioral manifestations of microsleeps include head nodding, slow eyelid closure, and eyelid drooping .
Drowsy driving has been compared with drunk driving in terms of its impact on performance [17-21]. After 24 consecutive hours of being awake, the level of impairment on the Psychomotor Vigilance Test (a test of sustained attention and vigilance, which measures the speed with which individuals respond to visual stimuli) resembles that seen in drivers with a blood alcohol of 0.08 percent, which is considered legally drunk across the United States. In driving simulator studies, sleep-deprived subjects have more lane (steering) deviations and more simulated crashes than well-rested subjects. Similar effects are well documented in patients with chronic sleep disruption due to untreated sleep disorders such as obstructive sleep apnea (OSA). (See 'Sleep apnea and other sleep disorders' below.)
Circadian factors also influence driving performance. Accidents in which drowsiness, rather than alcohol, is deemed to be a factor tend to coincide with times of highest sleep propensity: early morning (midnight to 7 AM) and mid-afternoon (3 PM) . This pattern is most obvious among the youngest drivers.
Inter-individual differences may also play a role in driving performance, as healthy adults show marked differences in neurobehavioral performance after sleep deprivation [23-25]. (See "Insufficient sleep: Definition, epidemiology, and adverse outcomes", section on 'Interindividual variation'.)
HIGH-RISK POPULATIONS — Although drowsy driving is a common problem that may arise situationally in any driver who is sleep deprived, certain groups are recognized to be at higher risk than others for habitual drowsy driving and its consequences, including teenage drivers, patients with sleep disorders such as obstructive sleep apnea (OSA) and narcolepsy, and commercial drivers (table 1).
Teenage and young adult drivers — Young drivers are at particularly high risk for drowsy driving-related crashes. In a study that examined over 4000 drowsy driving crashes, drivers aged 16 to 24, mostly males, accounted for over half of the crashes . Multiple factors may contribute to the risk of drowsy driving accidents among teens, including:
●A state of chronic sleep deprivation resulting from the combination of delayed sleep phase, with teens having a greater preference for later bedtimes and wake times, and early school start times. Over half of teenagers report getting less than the recommended number of hours of sleep per night (figure 1) [4,26-28]. (See "Delayed sleep-wake phase disorder".)
●Lifestyle factors, including homework, after school activities, sports, jobs, and social activities.
●Use of alcohol and other substances of abuse.
●Driving during times of day when sleepiness tends to be most pronounced, ie, morning and afternoon, during commutes to and from school, late nights on weekends, and following social events.
●An immature prefrontal cortex, with incompletely developed executive function and judgment. Executive function is essential during driving, as it helps maintain selective attention and parse complex data in sensory-rich environments, exercise effective judgment and decision-making, and recall recently-acquired information for immediate use (working memory).
●Greater susceptibility to the effects of sleep deprivation . On average, young adults respond faster than older adults. After sleep deprivation, however, younger drivers have much slower reaction times compared with older drivers, whose reaction times remain relatively resistant to sleep deprivation . Sleep deprivation can also impair executive function, leading to impulsivity, aggression, and risky decision-making .
Sleep apnea and other sleep disorders — OSA increases the risk of crashes by two- to threefold . In a meta-analysis of 16 observational studies, most of which were retrospective, the relative risk of crash in patients with OSA compared with controls was 2.4 (95% CI 1.2-4.9) . The most consistently identified factors associated with increased risk were body mass index, apnea-hypopnea index, and severity of hypoxemia. The presence of daytime sleepiness predicted risk of crash in some studies but not others, indicating that the absence of subjective sleepiness does not eliminate risk. Additional risk factors include advanced age and concomitant use of alcohol or sedatives.
Laboratory-based studies have shown impaired psychomotor vigilance and driving simulator performance in patients with untreated OSA [20,34]. In one study, performance of patients with mild to moderate untreated OSA was worse than those with a blood alcohol concentration of 0.06 percent . These effects can be seen in patients with and without daytime sleepiness and are magnified by concurrent use of alcohol or sedatives [34,35].
Patients with other sleep disorders may also be at increased risk for drowsy driving crashes, although data are more limited.
●Narcolepsy – One case-control study evaluated 70 control drivers and 424 drivers who had untreated sleep disorders including sleep apnea, narcolepsy, another sleep disorder with excessive sleepiness, or a sleep disorder without excessive sleepiness . Patients with narcolepsy were most likely to be involved in a sleep-related crash. (See "Treatment of narcolepsy in adults", section on 'Driving safety'.)
●Chronic insomnia – Insomnia may contribute to an increased risk of crashes [37,38]. In a population-based study of 54,399 adults in Norway followed for a median of 14 years, self-reported insomnia was associated with a two- to threefold increase in the risk of fatal crashes, independent of age, alcohol use, and medication use . The use of hypnotics for insomnia is another factor that may contribute to impaired driving in some individuals; particularly high-risk groups include women and older adults . (See "Treatment of insomnia", section on 'Dosing precautions'.)
Sedating medications and alcohol — Many classes of medications can cause drowsiness, including benzodiazepines, opioids, sedative hypnotics, barbiturates, antiemetics, anticonvulsants, antihistamines, anticholinergics, antidepressants, muscle relaxants, antipsychotics, anti-Parkinson medications, and hypoglycemic agents. These drugs pose risks for drowsy driving when used alone and especially in combination with other drugs, alcohol, or sleep deprivation.
Groups at particular risk are those receiving a new or increased dose of a sedating medication; those who are using multiple sedating medications concomitantly; those who are using sedating medications at high doses; and older adults .
One study in older adults found that the traffic accident risk increased by nearly 50 percent in the first week after starting benzodiazepine therapy . A population study of older drivers involved in traffic accidents resulting in hospitalization found that the use of benzodiazepines was associated with a fivefold increased risk for having a serious accident; increased risk was also associated with use of antidepressants (odds ratio [OR] 1.8) or opioids (OR 1.5) . (See "Approach to the evaluation of older drivers".)
The combination of alcohol or sedatives and sleep deprivation compounds drowsiness. In a laboratory-based study in which participants were restricted to four hours of sleep, consuming one unit of beer had the same impact that six beers would have in fully rested individuals .
Commercial drivers — Commercial drivers have been identified as a high-risk group for drowsy driving and its consequences. Contributing factors include sleep deprivation, overnight driving (at a time of peak sleep propensity), and high rates of comorbid OSA.
The National Transportation Safety Board in the United States estimates that drowsy driving is responsible for more than half of all crashes in which the operator of the truck is killed . Large truck crashes account for nearly 4000 deaths and 100,000 injuries per year in the United States, and approximately three-quarters of those injured or killed are occupants of other vehicles .
Sleep deprivation and self-reported drowsy driving is common in commercial drivers. In a poll of transportation workers, 20 percent admitted to driving a private vehicle while drowsy in the prior month . Another study found that 14 percent of long-haul commercial truck drivers sleep for an average of less than five hours per day . Train operators as a group had the highest rates of self-reported drowsy driving, with 39 percent admitting to driving while drowsy at least once in the prior month.
OSA is a common cause of daytime sleepiness and a known risk factor for drowsy driving and crashes. The reported prevalence of sleep apnea in commercial truck drivers is very high, ranging from 28 to 80 percent [47-49]. This high prevalence is probably because commercial truck drivers are disproportionately male, middle aged, and obese. (See 'Sleep apnea and other sleep disorders' above.)
Commercial drivers may require a higher standard for assessing medical fitness to drive compared with passenger car drivers , based on the fact that crashes involving commercial vehicles are more likely to result in the death of others on the road and carry a high cost [44,50-52]. (See 'Evaluation of drowsy drivers' below.)
Other high-risk occupations
●Medical house staff – Residents are at increased risk for drowsy driving accidents when working extended shifts and night shifts. In a prospective cohort study of 2737 interns who completed web-based surveys, interns who drove after an extended work shift (≥24 hours) were more likely to be involved in a fall-asleep crash (OR 2.3, 95% CI 1.6-3.3) or a near-miss incident (OR 5.9, 95% CI 5.4-6.3) than interns who drove after a normal work shift . For each extra monthly extended shift worked, the odds of a fall-asleep crash increased by 9 percent. These findings have been corroborated in driving simulator studies  and have contributed to duty hour regulations that limit the number of extended shifts and weekly hours worked for interns [55,56].
●Law enforcement officers – One study assessed nearly 5000 state and local law enforcement officers in the United States and Canada for sleep disorders and sleepiness . A total of 40 percent screened positive for a sleep disorder; 46 percent admitted to having fallen asleep while driving, and 26 percent stated that this happened one to two times during the past month. In another survey, 90 percent of police officers acknowledged that they considered drowsy driving to be as dangerous as drunk driving .
●Night or rotating shift workers – Night and rotating shift workers are at increased risk for errors and accidents, including crashes, due to insufficient sleep as well as the fact that they may be driving home in the early morning, at the trough of circadian alertness. In a real-vehicle investigation on a closed track, 38 percent of 16 post-night shift drives involved a near crash and 44 percent of drives had to be stopped early for safety reasons, compared with no near crashes or early terminations during 16 post-sleep drives . (See "Sleep-wake disturbances in shift workers".)
EVALUATION OF DROWSY DRIVERS — The goals for evaluating patients with self-reported drowsy driving and others who are at high risk are twofold: to identify patients with treatable causes of drowsiness who require further testing for diagnosis or who may benefit from disease-specific treatment, and to identify high-risk behaviors or habits that can be targeted for counseling.
The evaluation overlaps significantly with the approach to patients with excessive daytime sleepiness, which is reviewed in detail separately. Driving is a sedentary activity, and as such may bring to light previously unrecognized or unreported daytime sleepiness. A drowsy-driving crash or near-miss may be the first time a patient reports the symptom of excessive sleepiness to a health care provider. (See "Approach to the patient with excessive daytime sleepiness".)
Clinical history and risk factors — The history should include an assessment for the presence of common risk factors for drowsy driving, including (table 2):
●Sleep disorders (eg, obstructive sleep apnea [OSA], narcolepsy)
●Medical or psychiatric conditions which may interfere with sleep continuity and sleep quality (such as any cardiopulmonary disorders, pain syndromes, mood disorders)
●Use of sedating medications (eg, benzodiazepines, nonbenzodiazepine hypnotics, opioids) and alcohol
●Driving conditions (eg, long distance, late at night, lone driving)
●Circadian factors (eg, night or rotating shift work, jet lag)
●Lifestyle factors (eg, working multiple jobs, parenting infants)
●History of previous fall-asleep crash or near miss
The importance of many of these factors was verified in a population-based case-control study that included police data and telephone interviews of nearly 500 drivers involved in drowsy driving crashes and nearly 1000 control drivers . Compared with controls, drowsy drivers who crashed were more likely to report working multiple or nontraditional shifts, driving more often at night, obtaining fewer hours of sleep, poorer sleep quality and more daytime sleepiness, being awake for more consecutive hours, and having used sedating medications.
While most of these factors are apparent by history alone, OSA is common, yet often overlooked. Only about half of patients with OSA complain of excessive daytime sleepiness; other common symptoms include loud snoring, waking up choking or gasping, witnessed pauses in breathing during sleep, nocturia, and morning headaches (table 3). Physical exam findings suggestive of OSA include obesity, large neck circumference, crowded upper airway, and uncontrolled hypertension. (See "Clinical presentation and diagnosis of obstructive sleep apnea in adults", section on 'Clinical features' and 'Polysomnography and other testing' below.)
Polysomnography and other testing — Polysomnography or home sleep apnea testing is indicated in patients with suspected OSA . Given the high prevalence of undiagnosed OSA in high-risk groups such as commercial drivers, as well as evidence that treatment of OSA reduces the risk of crashes , there should be a low threshold to obtain testing in these individuals as well as in patients without other obvious causes of excessive sleepiness by history (algorithm 1). (See "Clinical presentation and diagnosis of obstructive sleep apnea in adults", section on 'Indications for diagnostic testing'.)
Additional indications for polysomnography in patients with daytime sleepiness include suspected narcolepsy (a diagnosis suggested by severe daytime sleepiness, cataplexy, sleep paralysis, sleep attacks, and hypnagogic or hypnopompic hallucinations) and clinical suspicion for other sleep-related breathing disorders such as central sleep apnea related to heart failure. (See "Approach to the patient with excessive daytime sleepiness", section on 'Additional testing' and "Clinical features and diagnosis of narcolepsy in adults", section on 'Clinical features' and "Clinical features and diagnosis of insomnia", section on 'Additional testing'.)
A comprehensive evaluation by a sleep specialist may be appropriate if the diagnosis is not immediately apparent; a host of medical conditions (eg, chronic pain, seizures, and mood disorders) and sleep disorders (eg, insufficient sleep, movement disorders, circadian rhythm abnormalities, and inadequate sleep hygiene, among others) may contribute to sleepiness while driving. (See "Approach to the patient with excessive daytime sleepiness".)
Laboratory-based assessments of sleepiness include use of driving simulators, psychomotor vigilance testing, multiple sleep latency testing, and maintenance of wakefulness testing. The potential advantage of such testing is that it provides objective data rather than subjective drowsiness assessment, which is recognized to be unreliable . However, results of these tests have not been validated as predictive tools for on-the-road performance, and normal results do not guarantee adequate alertness and safety, particularly on an ongoing basis. (See "Quantifying sleepiness".)
Special considerations in commercial drivers — Many states and countries have medical standards for commercial driving licensure that include specific questions about OSA and other sleep disorders, and some have implicit or explicit requirements for diagnostic sleep testing in commercial drivers with suspected OSA [32,63-65]. While no unified regulations exist to guide clinicians in testing, treatment, and re-evaluation of OSA in commercial truck drivers, guidelines are available from several groups [63,66-69], and recommendations have been summarized in a single document . These guidelines are conservative and may miss cases .
In the United States, a Joint Task Force of the American College of Chest Physicians, the American College of Occupational and Environmental Health, and the National Sleep Foundation has recommended that OSA testing be performed in commercial truck drivers with body mass index (BMI) ≥35 kg/m2 ; groups convened by the federal government have endorsed BMI thresholds ranging from ≥30 kg/m2 to ≥35 kg/m2 [66-69]. While lower BMI thresholds would likely capture more cases, given the very high prevalence of OSA in this occupational group, the threshold of ≥35 kg/m2 has been advocated to capture the more severe cases of OSA, which are more likely to result in a drowsy-driving crash, and also to limit the number of obese drivers who would be removed from service while undergoing evaluation.
Regardless of which threshold is chosen, use of an objective measure has been advised to select commercial drivers in need of diagnostic testing, rather than subjectively-reported symptoms obtained from the Commercial Driver Medical Evaluation form , as subjective reports are unreliable in this population [73-76]. (See "Quantifying sleepiness".)
PREVENTION AND COUNTERMEASURES — In addition to self-reported drowsy drivers, specific groups that should be targeted for education include teenage drivers, commercial drivers, those with sleep disorders, those taking sedating medications, night or rotating shift workers, and those with insufficient sleep, insomnia, and a history of habitual drowsy driving . (See 'High-risk populations' above.)
Key aspects of prevention and risk modification include education about symptoms of drowsy driving, avoidance and planning ahead, use of naps and caffeine when driving cannot be avoided, and treatment of any underlying causes of excessive sleepiness, such as obstructive sleep apnea (OSA). Patients should also be advised that self-assessment of drowsiness is unreliable, and that in the setting of inadequate sleep, they may be at risk even if they do not feel drowsy. Technological countermeasures may also play an increasingly important role in real-time recognition and prevention of drowsy driving, particularly since self-rating of performance can be inaccurate.
Driver education — Drivers should be educated about the symptoms and signs of drowsy driving and about effective countermeasures . Symptoms of drowsy driving include difficulty focusing, frequent blinking, heavy eyelids, daydreaming, wandering/disconnected thoughts, difficulty remembering the last few miles driven (sometimes called "automatic behavior") or missing exits and street signs, frequent yawning, rubbing eyes, difficulty keeping head up, drifting from lane to lane, tailgating or hitting a shoulder, and feeling restless and irritable [77,78].
Individuals should also be aware that the ability to self-rate sleepiness and performance is unreliable . Although performance continues to decline with cumulative days of sleep deprivation, subjective ratings of sleepiness tend to level off after the first few days in laboratory conditions of sleep deprivation , and drivers are often unaware of their own level of sleepiness .
Rather than driving while drowsy, drivers should be told to use other modes of transportation, such as ride sharing, public transportation, taxis, or walking. Importantly, drivers should be advised to plan ahead so that they avoid driving during times of day when they are likely to be sleepy, such as mid-afternoon, late at night, or after a period of sleep deprivation; to keep their trips short (under 20 minutes); and to use alternative modes of transportation.
All patients who have a sleep disorder that may contribute to sleepiness should be warned about the risk of driving while drowsy. Those patients who are considered high-risk (eg, those with excessive daytime sleepiness and a history of a drowsy driving crash or near miss) should be warned not to drive until therapy has been instituted and proven effective. A written information sheet is ideal (table 4).
Counseling about sedating medications — Drivers who use sedating medications should be warned about the risk of drowsy-driving crashes and advised not to consume alcohol in combination with such drugs. Individuals should be vigilant for symptoms that could indicate driving impairment, particularly during the titration period, including sleepiness, inattention, tremor, incoordination, confusion, gait instability, vision changes, fainting, or dizziness.
Individuals should also be advised to allow sufficient sleep opportunity following the use of sedating medications. Prescribing information for sedative hypnotic drugs such as zolpidem and eszopiclone contains specific warnings about the risk of next-day "sleep driving." This may be due to amnesia, microsleeps while driving, or a parasomnia characterized by a lack of awareness that they are operating a vehicle while under the influence of the drug. (See "Treatment of insomnia", section on 'Dosing precautions'.)
In addition to warning patients about the risk of drowsy driving, clinicians should also consider alternative nonsedating therapies, use the lowest dose required to achieve therapeutic effect, and modify dosing schedules when possible to limit drowsiness when the patient needs to drive. A clinician who considers prescribing a sedating medication should first conduct a careful analysis of potential risks, including drowsy driving, against the possible benefits of taking these drugs.
Naps and caffeine — The best countermeasure for combating drowsy driving is to obtain adequate sleep, as sleep debt can only be repaid with sleep [8,81]. Adequacy of sleep requires both sufficient sleep duration for age (figure 1) and restorative sleep quality. Therefore, any underlying sleep disorders should be treated effectively.
If patients experience drowsiness when driving, they should be encouraged to pull off the road to a safe area as soon as possible and sleep. Even a brief 20-minute nap can improve neurobehavioral performance after sleep deprivation . Longer naps may lead to sleep inertia, which can reduce performance during the first 30 minutes after waking .
Judicious use of caffeine can also help. Although caffeine use has not been studied formally in real-world driving conditions, laboratory-based studies of sustained sleep deprivation have found that reaction times, vigilance, and sustained attention improve after caffeine intake, particularly when combined with napping . Small quantities of caffeine taken over a longer period may be more effective than a single larger dose.
Other strategies commonly used to counter sleepiness, such as exposure to cold air, eating, drinking, and turning on the radio have not been shown to be helpful [8,81].
Treatment of sleep apnea — Treatment of OSA is an important part of prevention in both commercial and noncommercial drivers [32,63,84]. Patients with known OSA who report drowsy driving should be routinely asked about adherence with therapy, as nonadherence with continuous positive airway pressure (CPAP) therapy is common, and there are numerous strategies to address problems as well as alternatives to CPAP. (See "Adherence with continuous positive airway pressure (CPAP)".)
Meta-analyses of observational studies examining crash risk before and after initiation of CPAP therapy have found that treatment is associated with a significant reduction in the risk of crash (risk ratio [RR] 0.28, 95% CI 0.22-0.35)  as well as near-miss accidents (odds ratio [OR] 0.09, 95% CI 0.04-0.21) and crash-related events during driving simulator studies . Similar effects have been noted in patients treated with other therapies for OSA, including surgery and oral appliances, although data are more limited [86-89].
The management of patients with OSA is reviewed in detail separately. (See "Management of obstructive sleep apnea in adults".)
Role of prescribed stimulants — There is insufficient evidence to support use of stimulants or wake-promoting agents such as modafinil in unselected patients, and there is some concern that they might mask ongoing impairment in patients with sleep deprivation.
This was suggested by a study of eight healthy men and women who remained awake overnight on two separate occasions . Individuals were given a single dose of 300 mg modafinil or placebo and then underwent driving simulator testing two hours later. Compared with placebo-treated subjects, those treated with modafinil had fewer lane deviations on driving simulator testing, but other measures did not improve, including off-road deviations, reaction time to a concurrent task, and speed deviations. Despite this, subjects rated their own performance as improved. More studies are therefore needed before modafinil can be recommended for drowsy driving under conditions of sleep deprivation.
In patients with OSA, the use of stimulants is not routinely advised to reduce driving risk, given a paucity of evidence that benefits on driving performance would offset potential risks, including costs, side effects, less compliance with effective therapy such as positive airway pressure, and false reassurance .
In contrast, patients with severe hypersomnolence due to a primary sleep disorder such as narcolepsy are routinely treated with stimulants or wake-promoting agents to improve daytime alertness. For such patients, a decision to continue driving should be made in consultation with the treating provider. (See "Treatment of narcolepsy in adults", section on 'Daytime sleepiness' and "Treatment of narcolepsy in adults", section on 'Driving safety'.)
Audio-tactile lane markings — Milled-in strips of road ("rumble strips") or raised profile-lane markings, which increase the noise made by tires, have been installed on many roads with the goal of awakening an asleep driver or alerting an inattentive driver. Since drowsy diving crashes tend to be off-road or lane deviations, these strips are usually placed along the edge of roads or along centerlines. They may also be placed across lanes when speed reduction is required. Rumble strips were deemed cost-effective and were estimated to reduce accidents due to off-road deviations by 20 to 50 percent . Strips down the center and the edges of the road were shown to be more effective than either used alone .
Future technological countermeasures — A variety of technological countermeasures have been developed or are being developed to recognize and prevent drowsy driving.
●On-board assessment of driver fatigue – One of the first validated technologies to detect drowsiness in drivers uses a camera to measure percentage of eyelid closure over the pupil (PERCLOS) . The system calculates the proportion of time in a minute that the eyes are at least 80 percent closed . Another system detects changes in heart rate and respiration using sensors in the seat cushion and seatbelt to predict when a driver may be drowsy . Still others are investigating steering wheel variability as a predictor of drowsy driving .
Software applications compatible with smartphones have been developed, which use both forward- and rear-facing cameras to assess lane tracking, braking distance, and facial features or eyelid closure to warn the driver when they may be distracted or drowsy . A host of metrics have been suggested, and further study is needed to determine the optimum metric or combination of metrics and assess the impact of the system in reducing crashes in various groups. Available data suggest that a successful detection system will likely track multiple, rather than single measures .
●On-road crash prevention technologies – Crash prevention technologies are being offered more commonly in newer vehicles, including some trucks . The Insurance Institute for Highway Safety (IIHS) has estimated that these technologies may lower fatalities and injuries , although data are limited.
These technologies include warning systems (for lane departure, forward collision, and blind spots), assisting devices (for automatic braking and correction of lane deviation), and adaptive headlights. Forward-facing cameras track lane markings to assess when the vehicle moves out of lane. Light detection and ranging technologies assess braking distance, and may engage the brakes if the driver fails to respond to an alert. The alerts may include a dashboard warning light, a chime or sound, or vibration of the steering wheel.
●Driverless cars – The Insurance Agency for Highway Safety estimates that if auto-driving technologies were implemented in all vehicles, 33 percent of fatal crashes and 20 percent of accidents resulting in injuries could be avoided altogether or have their severity mitigated. These technologies may eventually be offered for trucks as well as passenger vehicles.
LEGAL CONSIDERATIONS — Individuals are expected to avoid driving while sleepy, regardless of whether the fatigue results from simply being tired or from a sleep disorder. Although laws vary by state and country, in general, an individual may be held civilly liable for falling asleep and criminally liable if the individual was aware of the risks associated with the sleep disturbance and did not take measures to reduce the risks. A list of states in the United States with current and pending drowsy driving laws is available .
All patients who have a sleep disorder should be warned about the risk of driving while drowsy (table 4) (see 'Driver education' above). In general, clinicians who fail to inform a patient of his or her risk of injury due to a medical condition or its treatment may be held liable to the patient if an injury occurs subsequently .
Deciding whether to report an individual who has had a fall-asleep crash or who continues to drive despite what appears to be an unsafe level of sleepiness can be challenging. Drivers who fear being reported may fail to return for follow-up care, and so fail to achieve the benefits of treatment and remain at risk for drowsy driving.
Because laws regarding the reporting of impaired driving to licensing authorities vary by location, clinicians should become familiar with rules governing their state or country. Some states mandate reporting of unsafe drivers, while others permit (without necessarily mandating) violation of doctor-patient confidentiality, if a physician believes it is in the best interest of the patient or the public safety. When determining whether to report, clinicians may have to weigh conflicting guidelines: a professional obligation to report and a legal requirement to maintain confidentiality, even in the face of danger to the public . An expert panel of the American Thoracic Society advocates reporting "if a highest-risk patient (eg, severe daytime sleepiness and a previous motor vehicle crash or near miss) insists on driving before the condition has been successfully treated or fails to comply with treatment requirements" .
Commercial drivers are generally held to a higher standard of medical fitness than noncommercial drivers, and in many cases, this includes considerations about known or suspected obstructive sleep apnea (OSA) or other sleep disorders such as shift work sleep disorder and chronic insufficient sleep, which may increase risk of drowsy driving. Sleepiness in long-haul commercial vehicle drivers carries great risk, as these operators spend many hours driving continuously in monotonous, sedentary conditions, in heavy vehicles, and sometimes late at night; yet, being unable to drive can be financially ruinous. Regulations and requirements for licensure may vary by state and country, and clinicians involved in the care of these individuals may find useful guidance in a task force report from the American College of Chest Physicians and others  as well as the Federal Motor Carrier Safety Administration website. The Truck Safety Coalition in the United States also compiles updated information on current and pending efforts with regard to drowsy driving.
SUMMARY AND RECOMMENDATIONS
●Drowsy driving and fall-asleep crashes are common and often result in severe consequences, including fatalities, because drivers fail to use maneuvers to avoid or mitigate crash severity. Approximately 40 percent of drivers admit to having nodded off or fallen asleep while driving in the past year, and about 25 percent admit to habitual drowsy driving (eg, at least once per month). (See 'Epidemiology' above.)
●Drowsiness impairs a host of cognitive functions that are important for driving, including judgment, attention, executive function, cognitive processing speed, memory, reaction time, and muscular coordination. (See 'Effects of drowsiness on driving' above.)
●Although drowsy driving is a common problem that may occur in any driver who is sleep deprived, certain groups are recognized to be at higher risk than others for habitual drowsy driving and its consequences, including teenage drivers, patients with sleep disorders such as obstructive sleep apnea (OSA) and narcolepsy, night shift workers, and commercial drivers (table 1). Use of sedating medications and alcohol, particularly in combination with sleep deprivation, also poses risks. (See 'High-risk populations' above.)
●Patients with self-reported drowsy driving, including those with a history of a fall-asleep crash or near miss, should be evaluated to identify treatable causes of drowsiness and high-risk lifestyle behaviors or habits that can be targeted for counseling and prevention. The history should focus on risk factors as well as symptoms and signs suggestive of OSA or other sleep disorders (table 2). (See 'Clinical history and risk factors' above.)
●Polysomnography or home sleep apnea testing is indicated in patients with suspected OSA, which is often undiagnosed and represents an important and treatable risk factor for drowsy driving and its consequences. Laboratory-based assessments of sleepiness, such as driving simulators, psychomotor vigilance testing, multiple sleep latency testing, and maintenance of wakefulness testing are not routinely indicated, as they have not been validated as predictive tools for on-the-road performance, and normal results do not guarantee adequate alertness and safety. (See 'Polysomnography and other testing' above.)
●Key aspects of prevention and risk modification include education about symptoms of drowsy driving, avoiding driving when drowsy, use of naps and caffeine when driving cannot be avoided, and treatment of any underlying causes of excessive sleepiness, such as OSA. Technological countermeasures may also play an increasingly important role in real-time recognition and prevention of drowsy driving. (See 'Prevention and countermeasures' above.)
●All patients with a sleep disorder that can cause sleepiness should be warned about the risk of driving while drowsy (table 4). Although specific laws vary by state and country, in general, clinicians who fail to inform a patient of his or her risk of injury due to a medical condition or its treatment may be held liable to the patient if an injury occurs subsequently. (See 'Legal considerations' above.)
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