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Updated 10:00 AM February 13, 2006




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Hold the phone: Several behaviors distract drivers

Talking to passengers may be just as dangerous for drivers as talking on a cell phone, U-M researchers say.

A study conducted at the U-M Transportation Research Institute (UMTRI) shows that drivers who have conversations with passengers exhibit similar levels of driving performance as motorists who use cell phones. The study found no statistical difference in terms of drivers keeping in the correct lane or using proper steering behavior when talking on a cell phone or 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," says 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 says. "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 UMTRI colleagues Joel Devonshire and Carol Flannagan analyzed hundreds of short video clips of 36 motorists who drove cars equipped with cameras that recorded vehicle movement and driver behavior.

More than a third of the 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 the 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 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 and 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.

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