Mitigating effects of distraction: Drivers adjust speed and glance behaviour during secondary tasks in a driving simulator study

Guidelines for evaluating distraction by in-vehicle infotainment systems focus on metrics, such as the total eyes-off-road time (TEORT), where any gaze away from the road indicates inattention. Underlying principles stipulate that secondary tasks should be interruptible and paced by the driver, not the system. The study's rationale is that drivers can engage in secondary tasks without impairing driving, provided they adequately compensate and perceive all necessary information about the driving situation. A driving simulator study was conducted to investigate the effects of self-paced and system-paced secondary tasks of varying difficulty on gaze and driving behaviour during safety-critical car-following scenarios, and to identify factors associated with the occurrence of critical rear-end events. Participants ( N = 42) performed secondary tasks varying in pacing (self-paced vs. system-paced) and difficulty (easy vs. difficult) while driving. Results indicate that the pacing of the secondary task has no significant effect on the dependent measures, whereas under difficult task conditions, drivers reduce speed and exhibit lower, and thus more critical, time-to-collisions. Moreover, difficult secondary tasks lead to increased TEORT, with glances to the secondary task longer in total and maximum duration but fewer in number. In a model investigating factors associated with the occurrence of critical rear-end events, findings suggest that mean speed and number of glances are important risk factors. The fitted model outperformed TEORT in explaining critical events. The insights provide a foundation for developing a test method to assess driver attention and may inform revisions of guidelines for in-vehicle devices and driver monitoring systems.