The Effects of In-Vehicle Distraction Upon Driver Response During a Crucial Driving Maneuver

Hancock, P.A., Simmons, L., Hashemi, L., Howarth, H., & Ranney, T. (1999). The effects of in-vehicle distraction upon driver response during a crucial driving maneuver. Transportation Human Factors, 1(4), 295-309.

In this article, we report the effects of the presence of an in-vehicle distracter (a telephone, number-matching task) on driver reaction to a light-controlled stop. Ten volunteer drivers were asked to perform 60 repeated circuits of a closed-loop test track, in which each circuit represented and experimental trial. At the beginning of each trial, the driver was presented with a unique 7-digit memory set. In addition to the memory requirement, the first digit of the memory set was used during driving in the distracter task. On 30 circuits, which was 50% of the total trials, neither the distractor nor the traffic control device was activated. On 10 circuits, only the distracter task was presented, which required the driver to compair a presented number with the first digit of the memory set and to indicate either a match or a mismatch via touch-screen activation. On another 10 circuits, a standard traffic signal changed from green to red, requiring and immediate stop. On 10 circuits, both the distracter and the traffic control device were activated together. Drivers were asked to recall the entire 7-digit string at the end of every trial. The whole sequence was repeated at a slow, approximately 20 mph, and a faster, approximately 30 mph, speed. The order of circuits within each speed condition was randomized so that drivers were unable to predict the occurrence of either the distractor or the light activation. Results indicate slower break response times to the change in traffic control device (onset of a red light) in the presence of the in-vehicle distracter. However, drivers exhibited significantly shorter stopping times to this red light activation in the presence of the distracter. Despite this latter effect, the margin of safety, as represented by stationary distance from the intersection, was significantly reduced approximately by 25% in the presence of the distracter. In addition, there were variations in the distracter response accuracy and the digit-recall memory that affirmed the deleterious effects of a competing task at this critical driver decision point. These results are discussed in terms of erosion of a safety margin in the presence of in-vehicle sources of distraction that are expected to increase significantly in the face of unregulated proliferation of Intelligent Transportation Systems in-vehicle devices.

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