Secondary task solutions to acute and chronic automation-induced underload

• We examined a supplementary task’s acute and chronic effects on drivers under simulated L2 driving conditions. • Self-paced engagement in a supplementary task reduces mental workload related to a road monitoring task. • Trust in automation diverts attention from road monitoring to the supplementary task. • Chronic supplementary task engagement intensifies attention diversion and mental workload reduction. • Trust and familiarity with the driving environment improve hazard perception. Partially automated vehicles (PAVs) relieve human drivers from performing certain basic vehicle control tasks. The human driver remains responsible for automated system supervision despite such support systems. Therefore, long drives with partial automation can induce underload conditions, thereby increasing passive fatigue, impairing situational awareness (SA), and reducing response capacity. As a result, engaging in cognitively demanding tasks has been suggested as an underload countermeasure. The present study examined the acute and chronic effects of adding a Trivia-like Supplementary task as a cognitive non-driving-related task (NDRT) on mitigating driver’s underload and induced passive fatigue. Further, it assessed the impact of the Supplementary task engagement on drivers’ trust, attention and hazard perception (HP) during partially automated driving (PAD). Twenty-four participants were randomly assigned to one of two conditions: (1) PAD with the Supplementary task and notifications of upcoming hazards or (2) PAD with notifications of upcoming hazards only. Participants experienced two forty-minute monotonous driving sessions, one week apart. Each driving session included four latent but unmaterialized hazardous scenarios. The mental workload was evaluated via objective and subjective methods, passive fatigue was measured using KSS and HP, and attention was assessed via gaze behavior analysis. Contrary to our initial literature-based assumption that driving under PAD without engaging with a Supplementary task would lead to underload, we found that under simulated driving conditions, this monitoring driving task leads to overload rather than underload. Thus, in contrast to our expectations, including a Supplementary task did not counteract mental underload, but rather it relieved the drivers from the primary monitoring task, leading to a reduction in cognitive workload, especially in chronic circumstances. Additionally, both experimental groups maintained high and similar HP performance. The findings suggest that including a Supplementary task and other human–machine interface (HMI), functionalities can modify drivers’ behavior and attention allocation strategies over time in various ways, stressing the crucial importance of a mindful systems design to ensure driver attentiveness across continued usage.