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In the first of our three-part series about driver intoxication, we reveal how impairment persists for hours after blood alcohol concentration falls.
Optalert engaged KEA Technologies in Boston to conduct a comprehensive study on how impairment develops after consumption of alcohol. It involved 30 diverse participants with no sleep disorders or other potential confounding factors.
Each participant began at 10:00 a.m. with a BAC of 0.00%. Their baseline impairment was measured and then they consumed alcohol. This study did something very different to prior research: BAC and impairment were measured repeatedly over the entire day as the participant processed the alcohol. The test ended when they returned a BAC reading of 0.00% or eight hours had elapsed.
Impairment was measured with the Johns Test of Vigilance (JTV), created by Optalert founder and sleep science pioneer, Dr. Murray Johns.
The JTV is a 15-minute test that was refined over years to measure the precise form of psychomotor impairment that indicates a person is unfit to drive. The test participant sees three circles. Every 5 to 15 seconds, the circles momentarily change to diamonds and squares for 400 milliseconds. The participant must click a button each time the shapes change. Non-response within 2 seconds is recorded as an error of omission (EOO).
At a glance: BAC versus Impairment |
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Blood Alcohol Concentration (BAC) is the amount of alcohol in the bloodstream, typically measured as a percentage. For example, a BAC of 0.08% means there are 0.08 grams of alcohol per 100 millilitres of blood. Factors like bodyweight, metabolism, and alcohol tolerance influence how rapidly BAC peaks and declines. |
Impairment refers to the decline in a person’s mental or physical capabilities. This can affect essential driving skills such as reaction, decision-making, and coordination. Optalert defines impairment in its study through errors of omission in the Johns Test of Vigilance. This test tracks non-response to a visual stimulus, pinpointing moments when someone’s attention falters. |
The trajectory of BAC was unsurprising. On average, it peaked 1.5 hours after drinking alcohol and took about 6 hours to fall back to 0.00%.
However, people’s impairment lagged far behind, peaking about 5 hours after drinking alcohol – even in participants well below the legal limit for driving under the influence (DUI)!
This delay in impairment is striking because many drivers would assume they are “sober enough” to drive as their BAC begins to drop.
However, their psychomotor impairment will actually be increasing for many hours. This lag effect is a powerful reminder that drivers with a BAC under the legal limit may still be impaired. In turn, a driver monitoring system could detect this and enact countermeasures to improve road safety.
The difference between BAC and impairment can be attributed to how alcohol affects the brain and body.
After drinking, alcohol spreads quickly through the bloodstream. While BAC measures how much alcohol is in the blood at a given time, this elevated level of alcohol has yet to have full impact on the impairment levels. This is why we saw BAC peaking around the 90-minute mark in our study, but impairment rising far more slowly and persisting a lot longer. Many participants were significantly impaired above baseline even when they had returned to a BAC of 0.00%.
At Optalert, we are dedicated to advancing technology that improves road safety. Our team is continually researching new eyelid-based biomarkers to detect impairment and keep road users safe.
Contact Optalert to explore how we can work together to revolutionise the field of road safety.