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A landmark transportation study quantifies distracted driving.
By Tom Vanderbilt

When David Strayer’s children were younger, they would, as children do, sometimes make faces at passing drivers on family trips. One time, as he began to tell them that it wasn’t a good idea to distract a driver, as he usually did, he realized that the other driver didn’t even notice. “The person was on a cellphone,” says Dr. Strayer, a psychologist at The University of Utah. “He was not paying attention to what someone else was doing–he was completely zoned out.”


Above: A research participant being fitted with EEG electrodes, which measured brain activity while she undertook various tasks while driving in a car and in a simulator. The syringe contained water to make better connections.

Below: The research participant was asked to perform a variety of tasks while driving on surface streets in Salt Lake City, Utah, during the study. While she drove, a researcher monitored her activities and reaction times.


This has become the state of driving in America, where an estimated one in 10 drivers at any one time–the highest rate in the world–is on a mobile phone conversation while driving. You have all seen it: The driver fumbling for a number who weaves from side to side. The driver who conspicuously slows, less for safety than to compensate as his mental bandwidth is taken up with conversation. The driver ahead of you at a traffic light who, as her eyes dreamily swim up from a mobile device, seems mildly surprised to note the light has changed.

Few people have devoted as much time and intellectual energy to the problem of distracted driving as Strayer, who for more than a decade has studied the issue, bringing his findings to forums ranging from state legislatures to “The Oprah Winfrey Show.”

His latest research, at the behest of the AAA Foundation for Traffic Safety, does something entirely novel. By measuring drivers’ performance–reaction time, glances at objects in the driving environment, brain activity–as they engage in a number of different tasks, both while they were driving (in a simulator and an actual vehicle) and were not, Strayer has created a comparative distraction “index,” a kind of five-point category-scale ranking (as with hurricanes). The study assesses how much certain tasks and forms of technology actually affect drivers.

“This research is for the first time taking about five decades of work that’s been done in aviation psychology, and pulling it into the cockpit of a passenger vehicle,” says Jake Nelson, AAA’s director of traffic safety advocacy and research. Adds Peter Kissinger, CEO of the AAA Foundation: “There’s so much discussion and debate about distraction, and at the same time, so little research to inform that debate.”

Driving itself, we should remember, requires a base level of mental effort. “It’s category one, not category zero,” says Nelson. But what happens when you layer other activities on top of that? Do hands-free phones impair drivers less than hand-held phones? Is listening to the radio the same as listening to an e-mail read by a smartphone app? Is talking to your passenger worse than talking to your car’s voice-activated infotainment system?

The answers may surprise you. Phone conversations had essentially the same effect whether they happened on a hands-free or hand-held device (even as surveys show a majority of motorists believe hands-free to be safer). An audio book required more mental workload than the radio. “Speech-to-text” systems were much more demanding–a “category 3” distraction (as Strayer describes, “you could just look at someone and know they were distracted”)–than simply listening to the radio or talking on the phone. Strayer suggests it may involve the lack of “backchannel” communication, those conversational cues we get from talking to real people—the same way, he suggests, we often stumble a bit when trying to leave a voice mail message.

The absolute highest level of workload came during the so-called “Operation Span” exercise, which requires people to do a series of math and memory tasks. Doing this while driving can actually hurt your head–and I speak from experience here, having struggled through it while trying to drive in a simulator in Strayer’s lab. The more I tried to focus on driving, the less I was able to recall; the more I tried to recall, the worse my driving became.

But what in the real world of driving is even remotely similar to Operation Span? Strayer wondered the same thing. Then he considered a new car he had taken out on a test drive. The infotainment features included a system for booking movie reservations. “You’re not sure what’s playing, what times are available, what theaters,” he says. “You reserve your seat, give your credit card info–that entire series of operations is going to be at least a category 3, and it wouldn’t surprise me if some of those pushed into category 4.” All of this is happening while the driver’s eyes are on the road and their hands on the wheel. But, as the phenomenon of “inattention blindness,” or the ability to miss something right in front of you, has shown, people who seem to be paying attention can be distracted. “Eyes off the road is a bad thing,” says Strayer. “It’s just that eyes on the road doesn’t mean it’s safe.”

And it’s the increasing availability, and complexity, of in-car, voice-activated technologies–integrating any number of smartphone-style applications, most having little to do with driving–that prompted AAA to support Strayer’s work. Simply adjusting the temperature or interacting with GPS–activities connected with driving–can be themselves distracting. “When you get into the world of updating Facebook or Twitter, or booking a dinner reservation,” says Nelson, “these are things that ought not to be done while driving a car.”

Another issue, says Strayer, is what psychologists call “metacognition.” People who are distracted are often not aware they are distracted. That lack of awareness may grow even deeper as user interfaces become more seamless. As services like Facebook increasingly become part of the in-car landscape, the potential danger grows, not simply because more people will do it more often, but because, says Justin McNaull, who directs AAA’s state relations department, it seems to carry the tacit endorsement of the car manufacturers. Drivers, he says, think: “The manufacturers wouldn’t put it in there if it wasn’t safe.”

AAA supports legislative bans on texting while driving, and a ban on wireless use for drivers under 18–as well as a more general “personal responsibility” call to not engage in these behaviors while driving. However, Nelson says, the current research does not call for a ban on voice-activated technology. Rather, it’s trying to address the potential dangers of a still-emerging technology before it becomes widely adopted. “We simply want to throw a flag down on this play and say, ‘Hey, we’ve learned something new here that we want to sit down and talk about,’ ” he says.

Tom Vanderbilt writes for many publications, including The Wall Street Journal, Wired and Smithsonian. His most recent book is the New York Times bestseller Traffic: Why We Drive the Way We Do (and What It Says about Us). He also writes the “Transport” column for Slate and is a visiting fellow at NYU’s Rudin Center for Transportation Policy.

Jul/Aug 2013 Issue



Understanding the Risks

Due to incomplete data, no one knows exactly how many crashes are caused by driver distraction, but it contributes to thousands of crashes and deaths. The National Highway Traffic Safety Administration (NHTSA) estimated that inattention was a factor in up to 9 percent of motor vehicle crashes in 2010.

The AAA Foundation for Traffic Safety, which has sponsored research on distracted driving since the early 1990s, analyzed data from a 2006 study conducted by Virginia Tech’s Transportation Institute that revealed that taking your eyes off the road for more than two seconds doubles your risk of a crash.

Yet despite strong scientific evidence and public awareness of the danger posed by distraction, research by AAA has shown the public maintains a strong “do as I say, not as I do” attitude toward distracted driving and many other driving activities/behaviors. According to the AAA Foundation’s 2011 Traffic Safety Culture Index, 79 percent of motorists rated texting while driving and 58 percent rated cell phone use very serious threats to their safety, yet many admitted performing these distracting behaviors while driving within the previous month.

For more details about distraction, visit



Tips to Stay Focused

Driving is a full-time job; it requires your full attention. Always focus on the important task of driving, and avoid any kind of distraction while behind the wheel.

As a general rule, if you cannot devote your full attention to driving because of some other distracting activity, take care of the other activity before or after your trip, not while behind the wheel. AAA offers these other helpful tips:

  • Plan ahead. Read maps and check traffic conditions before you get on the road.
  • Adjust seats, mirrors, climate controls, sound systems and other devices before you get underway.
  • Stow electronic devices. If you must call, text, or e-mail, pull over and park in a safe place first.
  • Secure children and pets before getting underway. If they need your attention, pull off the road safely to care for them.
  • Eat meals or snacks before or after your trip, not while driving.
checking phone


How to Measure Distraction

Led by David Strayer, Ph.D., professor of cognition and neural sciences at The University of Utah, his team of researchers set out to create an index of how much tasks and vehicle technologies affect driving. The study, “Measuring Cognitive Distraction in the Automobile,” has been hailed as groundbreaking research.

Working with University of Utah students, Dr. Strayer’s team fitted participants with head-mounted devices that showed lights flashing in the periphery of their fields of vision. They were asked to press a button with their thumb when the device presented a green light and do nothing when it flashed a red light–while performing various distracting tasks.

Researchers also used sensors and high-resolution cameras to track participants’ reaction times, brain activity, and eye movements to measure their responsiveness to the lights as their mental workloads increased.

In the first experiment, participants were asked to respond to the lights while viewing an image on a computer screen. The second experiment had participants respond while seated in a driving simulator. The third experiment measured participants’ responses to the flashing lights while they drove on quiet streets in suburban Salt Lake City, Utah.

In each experiment, the participants began by performing the “single task,”–i.e., viewing the image on the screen, “driving” in the simulator and driving through the suburbs–and then repeated the exercise while engaging in progressively more distracting activities in the following order: listening to the radio; listening to an audio book; talking to a friend or family member on a hand-held mobile phone; talking on a hands-free mobile phone; interacting with a speech-to-text program; and attempting to solve simple math problems while remembering the sequence of random words presented to them in between each math problem, the so-called Operation Span (OSPAN) exercise (designed to “max out” their mental workload).

Levels of distraction for each activity while driving, on a scale of 1 (least distracting) to 5 (most distracting) are as follows:

Category 1 (low level of mental workload)

  • Listening to the radio
  • Listening to an audio book

Category 2 (moderate level of mental workload)

  • Conversing on a hand-held phone
  • Conversing on a hands-free phone

Category 3 (high level of mental workload)

  • Interacting with a speech-to-text device

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