"Drowsy driving" episodes are quite commonly reported by drivers in the general community and by professional drivers. A recent population-based survey in USA indicated that 37% of the driving population had driven while drowsy and had dozed off at the wheel, some many times, within the preceding year. Only a minority of such episodes had caused a crash or near-miss incident.
Such an experience may lead drivers to believe that episodes of "drowsy driving" are readily manageable and are not necessarily associated with greatly increased risks. Combine that with the known impairment of the drowsy driver's ability to make sound judgements about driving risks (or anything else) when in the drowsy state, and the combination becomes potentially lethal. It has not been demonstrated that those risks are associated with the state of fatigue, in the absence of drowsiness.
At-risk drivers
Under particular circumstances it is possible for anyone to fall asleep while driving. Drivers at highest risk for crashes due to drowsy driving include:
- Commercial truck drivers
- Late night shift workers
- Parents taking care of young children
- People with untreated sleep disorders
- Young drivers, especially males, under age 26
The consequences of drowsy crashes are often the most serious in terms of death, injuries and property damage. That is because the drowsy driver makes no attempt to avoid the impending crash. For instance, no brakes are applied and no reduction of speed occurs before the crash.
Are you aware of drowsiness?
Most people seem to be aware that if they remain awake for prolonged periods, especially longer than 24 hours, their sleep propensity will increase. They will also be more likely to doze off under circumstances in which they would not normally do so, especially when they intend to remain awake, as with driving.
Unfortunately, the relationship between the duration of prior wakefulness and sleep propensity is very variable between different people. Some do not become very drowsy after remaining awake for 24hrs -30hrs, as others do. By contrast, other people become drowsy after remaining awake for only 17hrs. Drowsy driving episodes often occur within the first hour or two of driving and they would presumably not be controlled by existing regulations to do with the hours of work.
Alcohol intoxication vs. drowsy driving
The impairment in driving skills caused by drowsiness is not the same as that caused by alcohol intoxication, but there are some similarities. Drowsiness generally increases as the blood alcohol concentration (BAC) increases, but alcohol has more widespread affects on psychomotor performance than can be attributed to drowsiness alone.
It is possible to measure a driver's BAC soon after a crash and to arrive at a reasonably accurate estimate of their BAC at the time of the crash. Hence the widespread use of breathalysers and blood samples for the measurement of BAC in drivers after they have crashed. It is not possible, however, to measure accurately and objectively what a driver's level of drowsiness was at the time of a crash by some later measurement of their drowsiness under different circumstances.
In a survey of road crashes in Utah that police investigators had determined were caused by the drivers "falling asleep at the wheel", 41% of those drivers said they were either not drowsy at all or were only "slightly drowsy" before the crash. Some may ascribe this to the drivers' reluctance to admit fault. Others may say that the driver's memory of having been drowsy was lost after the crash, for whatever reason. However, the large proportion of drivers who denied being drowsy must raise suspicions that at least some were genuinely unaware of their drowsiness at the time.
- Drowsiness warning signs
- Inattention
- Inability to keep the eyes open
- Not remembering the last few miles driven
- Having wandering or disconnected thoughts
- Drifting out of the lane or hitting rumble strips
Before getting on the road:
- Get enough rest before you drive - most adults need 7-9hrs of sleep
- Have a passenger to talk to and share the driving
- Avoid alcohol and sedating medications - check the labels or ask your doctor
- Plan to take a break at least every two hours when driving
A driver's own reports of drowsiness may underestimate objectively measured drowsiness, particularly at high levels, and this may distort their subjective awareness of risks associated with "drowsy driving".
Drowsiness-monitoring technology
Focusing on the needs of drivers, Optalert has developed a devise that takes the guess work out of drowsy driving. Optalert's leading-edge technology continuously measures drowsiness by detecting changes in eye and eyelid movements.
Tiny light emitters and receivers are built into the frames of Optalert glasses worn by the driver. The glasses are connected to the Optalert vehicle system, installed within the vehicle, which processes all the information being transmitted from the glasses. Whenever Optalert detects the onset of drowsiness - usually before the driver becomes aware of it - a loud beeping noise and a voice message warns the driver immediately.
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