Cell Phones Impair Drivers as Badly as Booze

SALT LAKE CITY, June 30 - Drivers chatting on cell phones are as impaired as drivers who are legally drunk, researchers here said.

Three of 25 drivers crashed during a simulation while they were talking on cell phones, but none of the same drivers crashed in the simulator while intoxicated, said David L. Strayer, Ph.D., of the University of Utah reported in the summer issue of Human Factors: The Journal of the Human Factors and Ergonomics Society.

It didn't matter whether the cell phone was handheld or hands-free, he and colleagues added. Drivers performed equally poorly with both, so the study authors grouped the data on both types together.

The study included 40 participants (25 men and 15 women) who were 22 to 34 years old. All had driver's licenses, and participants averaged eight years of driving experience. The majority (87%) reported that they sometimes used a cell phone while driving.

Each participant underwent three driving simulations in which the task was to follow and react to the car ahead of them, which braked intermittently. The first simulation was done for baseline data, the second was done while talking on a cell phone with a research assistant, and the third was done after consuming enough vodka and orange juice to reach a blood alcohol concentration of 0.08%, the legal definition of intoxication in most states.

The participants' performance while conversing on a cell phone differed significantly from baseline. First of all, there were three rear-end collisions (P<.05). In addition, their reaction time to the car braking ahead of them was 9% slower, the variability of their following distance increased by 24%, and they took 19% longer to get back up to speed after braking (P<.01 for all).

In contrast, no intoxicated participants rear-ended the car ahead of them. Compared with baseline performance, intoxicated drivers exhibited a more "aggressive" driving style. They followed closer to the vehicle ahead, often came to within four seconds of a collision, and hit the brake with 23% more force (P<.05 for all).

Although the pattern of behavior was different between the cell phone group and the intoxicated group, the data supported pervious findings that "indicate that when driving conditions and time on task are controlled for, the impairments associated with using a cell phone while driving can be as profound as those associated with driving with a blood alcohol level at 0.08%," the investigators said.

The lack of performance difference in drivers using handheld versus hands free phones suggests that the impairment comes not from having a hand occupied but from "the diversion of attention from the processing of information necessary for the safe operation of the vehicle," the researchers said.

The researchers were somewhat puzzled that the intoxicated drivers didn't perform more poorly, but they noted that the simulations were done in the morning when drivers were probably refreshed by a night of sleep, whereas most intoxicated drivers are out at night and are suffering from some degree of fatigue as well.

"With respect to cell phone use, clearly the safest course of action is to not use a cell phone while driving," the researchers concluded."

"However, regulatory issues are best left to legislators who are provided with the latest scientific evidence," they added. "In the long run, skillfully crafted regulation and better driver education addressing driver distraction will be essential to keep the roadways safe."

More than 100 million U.S. motorists use cell phones while driving, according to data from the Cellular Telecommunications Industry Association, the investigators said.

In addition, about 8% of motorists at any given time during the day are talking on cell phones, according to an estimate from the National Highway Traffic Safety Administration, the investigators added.