Are all conversations are harmful?
To address this question, I teamed up with my colleagues Frank Drews and Monisha Pasupathi to see how a conversation with a friend on a cell phone differed from a conversation with a friend when they were sitting next to the driver.
Here is how the study worked. Two friends came up to the laboratory to participate in an experiment. One was randomly selected to be the driver and the other was selected to engage in a conversation with the driver.
Participants drove in our high fidelity simulator on a section of highway with traffic. They were told to drive until they came to a rest area and then exit and park the vehicle.
When drivers were driving without conversing (the single-task condition), they had no trouble finding the rest area. When drivers were conversing with their friend in the vehicle (the dual-task passenger conversation condition), they also were successful in exiting at the rest area. But when drivers were talking on a cell phone (the dual-task cell phone conversation condition), 50% of the participants drove right past their exit! That's right, half of the drivers on a cell phone failed to take the correct exit.
Below are two composite videos from the study. The first is from drivers talking to their friend on a cell phone. The second is from drivers talking to their friend in the vehicle. See if you notice things that might help explain the difference between the two conversations (hint: the videos reveal several important differences between the driving conditions).
We also performed an analysis of the conversation and found that passengers and drivers altered their conversation based on the driving demands. Passengers also helped the driver navigate, point out hazards, and keep on task. This sort of real-time support based on the driving conditions was absent for cell phone conversations.
In fact, whereas cell phones increase the crash risk (by a factor of 4), having a passenger in the vehicle actually lowers the crash risk. So, not all conversations have harmful effects on driving.