'Hands free' isn't mind free - Drivers on cell phones are as bad as drunks
October 2006

Until now, the slowing of reaction time under multitasking conditions, referred to as the psychological-refractory-period (PRP) effect, has been studied mainly with simple tasks in laboratory settings. But a new research study presents a unique perspective of how the PRP effect pertains to driving, perhaps the most ubiquitous real-world task where non-optimal performance can have serious consequences.

The study was conducted by University of California, San Diego scientists Jonathan Levy and Harold Pashler, along with Erwin Boer of ERB Consulting. Forty students participated in the study, which involved driving a car simulator, composed of a large plasma screen, a steering wheel, and gas and brake pedals located on the floor.

In the simulation, students followed a lead car and were instructed to brake as soon as they saw the illumination of the lead car's brake lights (they were instructed to avoid gradual slowing even if it was possible).

While subjects performed the braking task, they occasionally were required to respond to a concurrent easy task, where a stimulus – either a light flash in the lead car's rear window or an auditory tone – was randomly presented once or twice. Participants indicated the stimulus' frequency, sometimes by pressing a key on the steering wheel once or twice and sometimes by saying aloud the words "one" or "two."

Subjects in the study braked more slowly when the easy task's stimulus was presented simultaneously or shortly before the brake lights, thereby demonstrating the PRP effect occurs with "real-world" tasks.

Participants were 174 milliseconds slower at braking when the two tasks occurred at the same time than when they were presented 350 milliseconds apart. While 174 milliseconds may sound tiny, it translates to 16 feet in a car going 65 mph.

Responses were just as slow with auditory stimuli (tones) and vocal responses compared to visual stimuli (light flashes) and manual responses, meaning that even tasks that do not have a visual or manual component (like hands-free talking) can still lower response times when driving.

"This study joins a growing body of research showing that 'freeing up the hands' does not result in faster brake response times," says Levy, the lead author on the project. He adds, "not everyone appreciates the processing cost while driving imposed by carrying out other tasks, even easy ones."

Drivers on cell phones are as bad as drunks say Utah psychologists who warn against cell phone use while driving.

Psychology Professor David Strayer, the study's lead author, adds: "Just like you put yourself and other people at risk when you drive drunk, you put yourself and others at risk when you use a cell phone and drive. The level of impairment is very similar."

"Clearly the safest course of action is to not use a cell phone while driving," concludes the study by Strayer, Drews and Dennis Crouch, a research associate professor of pharmacology and toxicology.

The study reinforced earlier research by Strayer and Drews showing that hands-free cell phones are just as distracting as handheld cell phones because the conversation itself – not just manipulation of a handheld phone – distracts drivers from road conditions.

Human Factors Editor Nancy J. Cooke praised the study: "Although we all have our suspicions about the dangers of cell phone use while driving, human factors research on driver safety helps us move beyond mere suspicions to scientific observations of driver behavior."

The study first gained public notice after Strayer presented preliminary results in July 2003 in Park City, Utah, during the Second International Driving Symposium on Human Factors in Driver Assessment, Training and Vehicle Design. It took until now for the study to be completed, undergo review by other researchers and finally be published.

Different Driving Styles, Similar Impairment

Each of the study's 40 participants "drove" a PatrolSim driving simulator four times: once each while undistracted, using a handheld cell phone, using a hands-free cell phone and while intoxicated to the 0.08 percent blood-alcohol level after drinking vodka and orange juice. Participants followed a simulated pace car that braked intermittently.

Both handheld and hands-free cell phones impaired driving, with no significant difference in the degree of impairment. That "calls into question driving regulations that prohibited handheld cell phones and permit hands-free cell phones," the researchers write.

The study found that compared with undistracted drivers:

1. Motorists who talked on either handheld or hands-free cell phones drove slightly slower, were 9 percent slower to hit the brakes, displayed 24 percent more variation in following distance as their attention switched between driving and conversing, were 19 percent slower to resume normal speed after braking and were more likely to crash. Three study participants rear-ended the pace car. All were talking on cell phones. None were drunk.
    
2. Drivers drunk at the 0.08 percent blood-alcohol level drove a bit more slowly than both undistracted drivers and drivers using cell phones, yet more aggressively. They followed the pace car more closely, were twice as likely to brake only four seconds before a collision would have occurred, and hit their brakes with 23 percent more force. "Neither accident rates, nor reaction times to vehicles braking in front of the participant, nor recovery of lost speed following braking differed significantly" from undistracted drivers, the researchers write.

 "Impairments associated with using a cell phone while driving can be as profound as those associated with driving while drunk," they conclude.

Are Drunken Drivers Really Less Accident-Prone than Cell Phone Users?

Drews says the lack of accidents among the study's drunken drivers was surprising. He and Strayer speculate that because simulated drives were conducted during mornings, participants who got drunk were well-rested and in the "up" phase of intoxication. In reality, 80 percent of all fatal alcohol-related accidents occur between 6 p.m. and 6 a.m. when drunken drivers tend to be fatigued. Average blood-alcohol levels in those accidents are twice 0.08 percent. Forty percent of the roughly 42,000 annual U.S. traffic fatalities involve alcohol.

While none of the study's intoxicated drivers crashed, their hard, late braking is "predictive of increased accident rates over the long run," the researchers wrote.

One statistical analysis of the new and previous Utah studies showed cell phone users were 5.36 times more likely to get in an accident than undistracted drivers. Other studies have shown the risk is about the same as for drivers with a 0.08 blood-alcohol level.

Strayer says he expects criticism "suggesting that we are trivializing drunken-driving impairment, but it is anything but the case. We don't think people should drive while drunk, nor should they talk on their cell phone while driving."

Drews says he and Strayer compared the impairment of motorists using cell phones to drivers with a 0.08 percent blood-alcohol level because they wanted to determine if the risk of driving while phoning was comparable to the drunken driving risk considered unacceptable.

"This study does not mean people should start driving drunk," says Drews. "It means that driving while talking on a cell phone is as bad as or maybe worse than driving drunk, which is completely unacceptable and cannot be tolerated by society."

Driving while Distracted: A Growing Problem

The researchers cited figures from the Cellular Telecommunications Industry Association indicating that more than 100 million U.S. motorists use cell phones while driving. The National Highway Transportation Safety Administration estimates that at any given moment during daylight hours, 8 percent of all drivers are talking on a cell phone.

"Fortunately, the percentage of drunk drivers at any time is much lower," Drews says. "So it means the risk of talking on a cell phone and driving is probably much higher than driving intoxicated because more people are talking on cell phones while driving than are driving drunk." The main reason there are not more accidents is that "92 percent of drivers are not on a cell phone and are compensating for drivers on cell phones," he adds.

Cell phone use is far from the only distraction for motorists. The researchers cite talking to passengers, eating, drinking, lighting cigarettes, applying makeup and listening to the radio as the "old standards" of driver distraction.

"However, over the last decade many new electronic devices have been developed, and they are making their way into the vehicle," the researchers write. "Drivers can now surf the Internet, send and receive e-mail or faxes, communicate via a cellular device and even watch television. There is good reason to believe that some of these new multitasking activities may be substantially more distracting than the old standards because they are more cognitively engaging and because they are performed over longer periods of time."


 

Bibliography:

1. National Highway Traffic Safety Administration 
2. National Safety Council
3. Transport Research Laboratory