Counteracting driver fatigue in the context of conditional automated driving: an individualized and overarching approach

Driver fatigue is a major contributing factor to road accidents, often resulting in serious injuries or fatalities. In the context of conditional automated driving (CAD, SAE Level 3), where the driver assumes a passive role for extended periods, addressing fatigue becomes particularly critical. Therefore, this study aimed to investigate the effectiveness of an individualized combination of in-vehicle features as a countermeasure to driver fatigue during CAD, and its impact on subsequent manual driving performance. A total of 82 participants completed two manual drives, separated by a conditional automated drive, with the application of either an individualized, standardized, or without any in-vehicle features as driver fatigue countermeasure. In the countermeasure conditions, a combination of in-vehicle features was activated once participants reached a value of 7 on the Karolinska Sleepiness Scale (KSS) during CAD. After five minutes of applying the countermeasure, the participants were prompted to take over and continue driving manually. The application of in-vehicle features—whether standardized or individualized—significantly reduced self-reported fatigue during CAD compared to the no-countermeasure condition. However, no lasting effects were observed after the takeover to manual driving. Fatigue levels and driving performance were significantly worse in the second manual drive compared to the first, with no differences between the countermeasure groups. These findings suggest that while a combination of in-vehicle features (regardless of standardization or individualization) can temporarily mitigate driver fatigue during CD, it does not offer sustained benefits once manual control resumes. This underscores the need for continued development of driver fatigue countermeasures that extend beyond the automated drive.