This research assessed the impact of vehicle automation on a driver’s ability to anticipate latent threats and to detect materialized hazards on the forward roadway. In particular, the minimum alert time before transfer of control was determined. This was the minimum time required after an autonomous driving suite (ADS) had been in full control of a vehicle for the driver to reacquire the same level of situation awareness that he or she had when in full control of the vehicle. This simulator study included five treatment conditions during which drivers either were always in complete control of their own vehicle (control) or were required to resume control at 4 s, 6 s, 8 s, or 12 s before the appearance of a latent hazard (transfer). While the vehicle was in autonomous mode, the drivers performed an in-vehicle task for more than a minute and were told not to glance at the forward roadway. Analysis of eye movements showed that drivers in the control condition detected nearly 40% more hazards compared with drivers in the shortest transfer condition. The results indicated how long before control was transferred from the ADS back to a driver that the driver should be told that a transfer would occur, if the driver were to have full situation awareness. Unlike previous studies, this study both ensured that the driver was not watching for hazards while the ADS was in control and used a measure of situation awareness (hazard anticipation) that was closely linked to the actual understanding a driver had of the threats present in a given scenario.

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Several studies have reported that excessively long glances away from the forward roadway elevated the risk of crashes. However, little research has been conducted to determine how long between glances inside the vehicle to perform a secondary task does a driver need to glance toward the forward roadway to detect threats present in or emerging from the forward roadway. To determine this length of time, the authors asked drivers to perform simulated in-vehicle tasks requiring seven glances alternating inside (four) and outside (three) the vehicle. The glance inside was limited to 2 s. The glance outside was varied between 1 and 4 s. Forty-five participants were evaluated across one continuous view and two conditions of alternating views (baseline and low cognitive load). Drivers in both conditions of alternating views were found to detect far more hazards when the forward roadway duration between two in-vehicle glances was the longest (4 s). The decrease in hazard detection during the shorter roadway durations was a consequence of the drivers' having to devote more resources to their driving while they switched their attention between the primary (driving) and secondary (in-vehicle) tasks. Type of processing was found to have an effect, with a larger percentage of the hazards detected in scenarios involving bottom-up processing (compared with top-down), while there was no significant effect found for eccentricity (central versus peripheral). The results suggest that a driver's minimum glance duration on the forward roadway must be at least 7 s when he or she is engaged in a low-load, in-vehicle task that requires alternating glances inside and outside the vehicle.

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