Evaluation of the Minimum Forward Roadway Glance Duration

Abstract

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.