Driving context influences drivers' decision to engage in visual-manual phone tasks: evidence from a naturalistic driving study

Journal article, 2015

Visual-manual phone tasks (i.e., texting, dialing, reading) are associated with an increased crash risk. This study investigated how the driving context influences drivers' decisions to engage in visual-manual phone tasks in naturalistic driving. Method: Video-recordings of 1432 car trips were viewed to identify visual-manual phone tasks and passenger presence. Video, vehicle signals, and map data were used to classify driving context (i.e., curvature, other vehicles) before and during the phone tasks (N=374). Vehicle signals (i.e., speed, yaw rate, forward radar) were available for all driving. Results: The drivers were more likely to engage in phone tasks while standing still, and less likely while driving at high speeds or executing sharp turns, or when a passenger was present. Lead vehicle presence did not influence how likely drivers were to engage, but they adjusted their task timing to situations when the lead vehicle was increasing speed, resulting in increasing time headway. The drivers adjusted task timing until after making sharp turns and lane change maneuvers. In contrast to previous driving simulator studies, there was no evidence of drivers reducing speed as a consequence of phone task engagement. Conclusions: The results show that experienced drivers are skilled at using information about current and upcoming driving context to decide when to safely engage in visual-manual phone tasks. However, drivers may fail to sufficiently increase safety margins to allow time to respond to possible unpredictable events (e.g., lead vehicle braking). Practical Applications: Advanced driver assistance systems should facilitate and possibly boost drivers' selfregulating behavior. For instance, they might recognize when appropriate adaptive behavior is missing and advice or alert accordingly. The results from this study could also inspire training programs for novice drivers, or locally classify roads in terms of the risk associated with secondary task engagement while driving.