Objectives Studies of devices detecting sleepiness need reference points of physiological sleepiness. The present study sought to validate the Karolinska drowsiness score (KDS) as an indicator of physiological sleepiness against driving impairment and eye blink duration during a 45-minute drive in an advanced moving-base driving simulator.

Methods Data from 19 persons were used in the analysis. Electrooculography, electroencephalography, and electromyography were administered continuously. Physiological sleepiness was quantified by scoring the percentage (0–100%) of the scoring epoch with alpha and theta activity and slow eye movements (KDS). Lateral position and speed were used as measures of driving behavior. Lane departure was defined as two wheels touching the lane markers. Blink duration was used as a secondary indicator of sleepiness.

Results The results showed that, for young drivers, sleepiness increased with time in the task with higher levels. The variability of the lateral position and the mean and variability of the blink duration significantly changed when sleepiness increased to KDS ≥20%. Furthermore, there was an increase in the risk of lane departure for KDS ≥30%.

Conclusions The results suggest that KDS scoring is a reasonable procedure for estimating physiological sleepiness under conditions of driving. The results also indicate that a younger age is associated with greater sensitivity to sleepiness at the wheel.

Key terms driver simulator study; driving behavior; driving impairment; lane departure; night; physiological sleepiness; risk; validation