2  The Effects of Driver Distraction

Consider the typical Hollywood driver distraction disaster scenario. The driver is tooling down the road, listening to a cassette tape, or eating a sandwich. The driver accidentally drops the tape or sandwich or whatever, and reaches down to get it and completely ignores what is happening on the road. When the driver looks up again: bang! A big rig, or train appears, and the driver dies.

There is this obvious danger of switching tasks so completely that the main driving task is ignored. Remembering that a car going 70 miles per hour travels over 100 feet in a second, we can see that it doesn’t take long for a disaster to occur. Yet, because people are very good at task-switching, there are some other results that are not necessarily obvious when there are distractions, including slower reaction time, decreased ability to see hazards, and a “shrinking operating envelope.”

Reaction time is the amount of time it takes us to move from perceiving to action. Usually, the faster we respond, the better, but when we distracted, the amount of time per task increases. This is a clear result of our attention being split between tasks, as well as the increased cost of switching between tasks. Because vehicles can be moving very quickly, even sub-second increases in reaction time can be dangerous. Because our attention is being split, it is also more likely that we will perceive fewer potential hazards while driving. The Hollywood scenario is the extreme of this, but, again, even missing one potential hazard in our visual field, for example, can be very dangerous.

The “operating envelope” is the space in which you feel safe to act. For example, while making a left hand turn, your brain makes very complicated calculations about how quickly oncoming traffic is arriving, and hence, how much space and time you have to act. When drivers are distracted, they tend to think they can act in a smaller amount of space and time then is actually safe, thus increasing the risk of an accident.