It has been known for some time that cell phones can lead to driving accidents. After watching the behavior of some other drivers on the road, I’m sometimes surprised that there aren’t more cell-phone-related accidents than there already are. With well over 100 million cell phone users in the U.S. alone, the problem isn’t going to get any smaller.
Until recently, there has been some dispute about exactly why cell phones are unsafe for drivers. Two high-profile studies in the 1990s suggested that any manual manipulation of devices in a car, including not only dialing a cell phone, but also adjusting the radio and other gadgets, led to poor driving. This has led to the rise of hands-free phones, voice-activated phones, and been accompanied by even more gadgets, including GPS, DVD players, and even video games in cars.
In 2001, however, David Strayer and William Johnson of The University of Utah conducted a study which helped narrow down precisely where the danger in cell phone use lies (“Driven to Distraction: Dual-Task Studies of Simulated Driving and Conversing on a Cellular Telephone,” Psychological Science, 2001).
In their first experiment, Strayer and Johnson had volunteers perform a simple simulated driving task: using a joystick to make a cursor to follow a dot moving randomly back and forth across the screen (though this reminds me of the primitive “games” I used to type into my Commodore-64 from computer magazines in the early 1980s, it’s a reasonable simulation of the cognitive demands of driving a car). At random intervals, the dot would turn either green or red. On a “red light,” participants were supposed to press the “brake” button on the joystick. After a practice round with no distractions, participants either had a conversation on a handheld or hands-free cell phone (what did they talk about? The issues of the day while the experiment was being conducted: the Clinton impeachment scandal or the Salt Lake City Olympics bribery scandal). A control group listened to the radio or an audiobook.
Strayer and Johnson found no difference between people who used a handheld or hands-free cell phone, and no difference between radio/audiobook listeners and the driving-only condition. However, the cell-phone talkers missed more than twice as many red lights as the other participants:
In addition to the accuracy problems, cell phone users also showed slower reaction times compared to when they were driving alone.
But does any conversation lead to driving errors? In a second experiment, Strayer and Johnson used a similar apparatus, but instead of using red and green lights, they had participants drive over “easy” and “difficult” courses. The volunteers were first asked to simply repeat words to the experimenter over the telephone. Next they were asked to generate a new word starting with the last letter of the word the experimenter gave them (for example if the experimenter said “salmon,” the volunteer could respond “nicotine”). The results were as follows:
Strayer and Johnson used a statistical method to measure the number of errors the drivers made. There wasn’t a significant difference in errors on the easy course, but on the difficult course, when drivers had to generate words in response, they made significantly more errors. So the key seems to be not simply that drivers are having a conversation, but that they are actively generating responses. In these conditions, drivers are more likely to make errors. If word of this result gets out to the gadget-makers, perhaps the next must-have phone will have a conversation analyzer that automatically warns you if you’re talking safely!