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Feb. 13, 2006

Road chat: Talking to passengers can be as dangerous as using a cell phone


ANN ARBOR, Mich.—Talking to passengers may be just as dangerous for drivers as talking on a cell phone, say University of Michigan researchers.

A new study by the U-M Transportation Research Institute shows that drivers who have conversations with passengers exhibit similar levels of driving performance as drivers who use cell phones. For example, the study found no statistical difference in terms of keeping in the correct lane or using proper steering behavior between people talking on a cell phone or those conversing with a passenger.

"This may suggest that talking on a cell phone, from a driving performance perspective, is no worse than holding a conversation with a passenger or taking part in a number of other potentially distracting behaviors," said James Sayer, an assistant research scientist at UMTRI.

Relative to driving performance when not engaged in anything but the task of driving, all forms of "non-driving" behavior resulted in at least some degraded performance, depending on the measure being considered.  

"The use of cellular telephones while driving receives a lot of attention in the popular press, probably because their popularity and widespread use is relatively new," Sayer said. "But the results of our study show that many of the other behaviors that drivers engage in, such as eating, drinking, grooming and having conversations with passengers, are potentially just as detrimental to driving performance."

Sayer and colleagues Joel Devonshire and Carol Flannagan studied the effects of secondary behaviors on normal, everyday driving performance. They analyzed hundreds of short video clips of 36 motorists who drove cars equipped with cameras that recorded vehicle movement and driver behavior for nearly four weeks each.

More than a third of the video clips showed drivers engaging in secondary tasks. Conversation with passengers was the most common (15 percent of the clips), followed by grooming (6.5 percent), cell phone use (5 percent) and eating and drinking (2 percent).

While all of the non-driving behaviors were associated with more erratic steering behavior, the researchers found that other measures of driving performance, such as lane position, speed fluctuation, use of the accelerator pedal and glance behavior (checking mirrors, looking out side windows, etc.), showed mixed results.  

For example, cell phone use did not affect speed variation, although frequency and duration of glances away from the road in front of a driver was lowest when using a cell phone—which could negatively affect scanning the roadway environment, they say.   Eating and drinking while driving had little effect on driving performance, except for modest increases in steering variance and glance frequency, as well as more frequent braking. They found a similar pattern for grooming behaviors.  

The study also showed that women and younger drivers (30 and under) were more likely to engage in secondary tasks. Female drivers were much more likely to converse with passengers, but men had higher rates of cell phone use and grooming behaviors.

In addition, the researchers examined contextual factors, such as road type, road curvature and road condition. They found that drivers performed differently when taking part in different tasks and appeared to selectively engage in secondary behaviors, depending on traffic and roadway conditions.

Previous research—using driving simulators and controlled on-road or test-track driving, rather than natural conditions—suggests that driving performance suffers when drivers engage in secondary behaviors.

"Until now, no published data has examined the effects of secondary tasks on driving performance measures under naturalistic conditions—drivers using instrumented vehicles in their daily lives—and few have examined the relative frequency with which these secondary behaviors even occur," Sayer said. "Nonetheless, there is a growing public concern with driver distraction, including state and local laws that impose penalties for engaging in distracting behaviors while driving.

"But our study showed relatively little effect of secondary behavior on basic driving performance measures. In fact, drivers may be performing secondary tasks when their driving skills are least needed and when the traffic environment tends toward being less challenging based upon a driver's own assessment."

For more information on UMTRI, visit: www.umtri.umich.edu.

Contact: Bernie DeGroat
Phone: (734) 936-1015 or 647-1847