The effect of driving demands on distraction engagement and glance behaviors: Results from naturalistic data

•Aim: To assess the relation between driving demands and distraction.•A naturalistic driving study dataset was used.•Environmental visual difficulty reduces distraction engagement and off-path glances.•Speed reduces distraction engagement when motor control difficulty is higher.•Drivers over 35 have lower rates of off-path glances compared to younger drivers. To understand drivers’ engagement in distractions and their visual attention allocation under different driving demands. Background: Although distraction increases crash risk, drivers engage in distractions frequently with no negative consequences, likely in part due to their self-regulating behaviors. Prior research revealed a variety of self-regulating behaviors specifically related to cell-phone engagement, but very limited research has investigated whether and how driving demands affect engagement in distractions in general, particularly within a natural setting rather than in the simulator. Method: We used the Naturalistic Engagement in Secondary Tasks (NEST) dataset, a subset of SHRP2 data, to analyze secondary task engagement and off-path (not in direction of travel) eye glances. In addition to assessing their relation to environmental demand, we also considered driver age and chosen speed. Results: Higher visual difficulty environments (characterized as visually complex and/or with low visibility) were associated with a decreased likelihood of secondary task engagement as well as a decrease in off-path glances, particularly longer ones (>2s). Drivers 35 and older had lower rates of off-path glances compared to younger drivers. An increase in speed was associated with a decrease in the likelihood of task engagement in higher motor control difficulty environments (characterized as poor surface condition and/or curved road) but not in lower ones. Conclusion: Drivers appear to modulate their task engagement and off-path glances based on driving demands. However, given that inopportune short off-path glances can lead to crashes, interventions are still needed to help drivers better modulate their distraction engagement.