Measuring with the JDS™

With 30 per cent of road fatalities attributed to drowsy driving, at Optalert we believe the Johns Drowsiness Scale (JDS™) will, in the near future, become as important as Blood Alcohol Concentration (BAC) readings.


What is the JDS™?

The Johns Drowsiness Scale (JDS™) is a 10-point scale developed by Optalert’s Founding Director, Dr Murray Johns, where a score of 0 = ‘very alert’ and 10 = ‘very drowsy’.

It is used to define the exact level of drowsiness experienced by operators using Optalert’s early-warning drowsiness detection products, which means you can now put a number on how “tired you feel?”.

Recent evidence has shown the JDS™ can be applied to other sensor technologies capable of measuring eyelid aperture, even at relatively low sampling rates.

What does a driver’s JDS™ score tell operators?

  • Score of 3 or above : the risk per minute of performance failure begins to increase only slightly as the score rises above 3
  • Score of 4.5 or above : this risk increases substantially
  • Score above 5 : the risk of performance failure (i.e. the risk of a drowsy crash) is sufficiently high, in fact, several times higher than for an alert driver

The ability to objectively identify the earliest signs of drowsiness removes uncertainty and subjective bias that can influence a professional operator’s judgment, even though they are expected to remain vigilant in the workplace.

JDS™ vs. BAC (Blood Alcohol Concentration)

Independent research has shown JDS™ scores at medium risk levels indicate performance impairment equivalent to a blood alcohol concentration of 0.05, the legal limit on roads in many countries.

High-risk JDS™ scores correspond to impairment equivalent to a BAC level of 0.08. These levels of impairment are similar to being awake for 17 and 21 hours respectively.

Like BAC readings, drowsiness can affect people very differently and while you may have had a good night of sleep the previous night, the cumulative effect of long periods of poor sleep could mean you should not be driving or making other critical decisions.

The only real way to tell if a person is alert enough to drive is to accurately measure them while driving and our system does this and gives early warnings to drivers who are at risk.

Our JDS™ scale, and our early-warning drowsiness detection products for measuring individual fatigue, work together to give valuable information to show when a driver needs to stop driving.

Performance failure

Peer-reviewed research has shown as levels of drowsiness increase, the risk of performance failure also increases.

The term ‘performance failure’ refers to the inability of a person to respond appropriately, such as failing to respond to a visual stimulus (for example, responding to a stop signal) or failing to turn the wheel during a bend in the road.

A drowsy driving accident will occur if a performance failure coincides with the need to perform a safety critical task.


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