In-vehicle fragrance administration as a countermeasure for driver fatigue.

Driver fatigue is a contributing factor in about 10-30% of all fatal crashes. Prevention of fatigue-related crashes relies on robust detection of driver fatigue and application of effective countermeasures. A potential countermeasure is fragrance administration since odors can have alerting effects on humans. The aim here was to investigate if a fragrance incorporating trigeminal components could be used as an in-vehicle countermeasure for driver fatigue. The fragrance was tested in a driving simulator with 21 healthy but sleep-deprived participants. Each participant performed a monotonous driving task twice, once with active fragrance containing a trigeminal component and once with olfactory fragrance, in a cross-over single-blind design. The order of trigeminal/olfactory fragrance was randomized and blinded to the participants. Both fragrances (trigeminal/olfactory) were administered either when the participant fell asleep (defined as eye closure > 3 s) or after approximately 45 min if the participant did not fall asleep. Self-reported sleepiness was assessed using the Karolinska Sleepiness Scale (KSS) every 5 min during driving. Variability in speed and lateral position and line crossing frequency were logged for each drive to measure driving performance. Heart rate measurements (ECG) and eye blinks (EOG) were collected to investigate potential arousing effects of the fragrance and to track objective signs of sleepiness. Mean blink duration, which was used as an objective measure of sleepiness, decreased significantly, after fragrance exposure, as did the frequency of line crossings, but there were no statistically significant differences between the fragrance with trigeminal stimulus and the pure olfactory fragrance. The results are in line with the effects found for other commonly used fatigue countermeasures, like playing loud music. These countermeasures can restore alertness and driving performance for a short while. Whether this is sufficient to support driving performance until the driver can make a safe stop in real traffic remains a topic for future studies.