The Effect of Cognitive Load on Drivers’ Visual Search Strategies During Partially Automated Driving in an Urban Environment

The implementation of Partially Automated Driving (PAD) systems is increasingly common in consumer vehicles. While these systems support longitudinal and lateral vehicle control, they still require drivers to monitor the environment and intervene when necessary. Therefore, drivers must continue to allocate their visual attention effectively and remain aware of potential hazards. However, increased engagement in non-driving-related activities (NDRAs) has been observed during PAD. While the detrimental effects of visual-manual NDRAs on drivers’ visual attention during PAD is well-established, the impact of cognitively demanding NDRAs that take drivers’ mind off but allow their eyes to remain on the roadway is poorly understood. It is also unclear how the effects of cognitive load vary across automation levels. A driving simulator study was conducted to examine drivers’ visual attention under cognitive load, induced by a 2-back task, during both manual driving and PAD. An urban section of road, with a range of vehicles and other road users as potential hazards, was used to study drivers’ allocation of attention. Results indicated that, during PAD, drivers adopted a broader visual search strategy, directing more attention to the peripheral driving environment. However, drivers’ visual search was more restricted under cognitive load, with attention concentrated on the road ahead, accompanied by fewer and shorter glances to the periphery, regardless of driving mode. These findings add knowledge on how cognitively demanding NDRAs affects drivers’ visual attention, under different driving automation levels, and highlight the need for targeted countermeasures to ensure drivers safely monitor PAD and the driving environment.