The objective of this study was to determine whether cell phone use by drivers leads to changes in the frequency of other types of potentially distracting behavior. There were two main questions of interest: (1) As each driver changes cell phone use, does he/she change the amount of driving time spent on other distracting behavior? (2) As each driver changes cell phone use, does he/she change the amount of driving time spent looking away from the driving task? Day-to-day driving behavior of 105 volunteer subjects was monitored over a period of 1 year. In-vehicle video was used to classify driver behavior. The amount of driving time during each trip spent on tasks secondary to driving (or looking away from the driving task) was correlated to the amount of time on a cell phone, taking into account the relationships among trips taken by the same driver. Drivers spent 42% of the time engaging in at least one secondary activity. Drivers were talking on a cell phone 7% of the time, interacting in some other way with a cell phone 5% of the time, and engaging in some other secondary activity (sometimes in conjunction with cell phone use) 33% of the time. Other than cell phone use, the most common secondary activities were interacting with a passenger (12% of driving time), holding but not otherwise interacting with an object (6%), and talking/singing/dancing to oneself (5%). Drivers were looking straight forward 81% of the time, forward left or right 5% of time, in a mirror 4% of time, and elsewhere (eyes off driving task) 10% of time. On average, for each 1 percentage point increase in cell phone talking, the other secondary behavior rate decreased by 0.28 percentage points (p-value <0.0001), and the rate of eyes off driving task decreased by 0.02 percentage points (p-value = 0.0067). For each 1 percentage point increase in the amount of other cell phone interaction per trip, the other secondary behavior rate decreased by 0.08 percentage points (p-value = 0.0558), but the rate of eyes off driving task increased by 0.06 percentage points (p-value <0.0001). For each 1 percentage point increase in secondary behavior other than cell phone use, the rate of eyes off driving task increased by 0.06 percentage points (p-value <0.0001). Taken together, these various effects imply that an increase in cell phone interaction time results in no change in eyes off driving task, despite an increase in overall time involving secondary behavior. Increases in the amount of driving time spent talking on a cell phone are associated with decreases in time spent on other distracting behavior and decreases in eye glances not related to the driving task. Although using a cell phone can be distracting from the driving task, other secondary activities can be equally or more distracting, at least as measured by eye glances away from the road ahead and mirrors. In this group of drivers, the increased eyes off driving task associated with dialing, reaching for, and answering the cell phone was offset by the decrease in eyes off driving task associated with talking on the phone. Overall, the results are consistent with the lack of a dose-response relationship between population cell phone usage rates and crashes. They indicate that predictions about the effect of cell phone usage on driver distraction need to consider what other behavior is being displaced by the time spent on the phone. Focusing only on the distraction of using cell phones while driving may lead drivers to disregard the risk of other secondary behavior that is even more distracting. (Author/publisher)
Abstract