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Chatting with passengers distracts drivers and significantly increases the risk of having an accident.

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Shut Up! I'm Driving

Add an unlikely item to the list of road hazards. Sure, cell phones, big SUVs, and tailgaters are dangerous--but keep your eyes peeled on the carpool lane, too. New research shows that drivers with a passenger in their vehicles up their risk of an accident by 60%. Two or more passengers double the odds.

Driving simulations and laboratory studies show that talking on cell phones and text messaging increase a driver's risk of a crash. But only a few studies look at what really happens out on the roadways. Previous studies found that drivers using cell phones were four times more likely to have an accident than those who weren't yakking on their mobiles. Medical epidemiologist Suzanne McEvoy of the University of Sydney, Australia, wondered how that compared to having passengers in the car.

McEvoy and colleagues went to local hospitals and interviewed accident victims who came into the emergency room. They collected data on 274 people who had non-life-threatening injuries from an automobile accident, asking them how many passengers they had been carrying and whether they were interacting in some way with the passengers. They compared these volunteers to 1096 drivers they recruited from the nearest gas stations to the accidents at the same time of day and day of the week, who served as a control group. The researchers also acquired cell phone records so they could verify calls made near the time of the accidents.

The team found that having at least one passenger in the car increased the risk of the driver getting into an injurious accident by 60%, about the same increase in risk as incurred on wet roads. Roughly a third of the injured drivers reported talking or interacting with the passenger in some way at the time of the accident. Having two or more passengers doubled the risk of an accident. The researchers also found that, as expected, talking on the phone quadrupled the risk of having an injurious accident. Talking on the phone is more dangerous, McEvoy speculates, because passengers are at least aware of the traffic conditions and can stop talking when things get rough. This is the first time such comparisons have been made in the same real-life situations, the authors report today in Accident Analysis and Prevention.

Passengers are not always a problem, points out cognitive psychologist Frank Drews of the University of Utah, Salt Lake City. In laboratory studies, Drews has found that some passengers help drivers avoid accidents by paying attention to traffic. The new study was too small to explore that distinction, Drews says, so further research would be necessary before suggesting policy decisions for drivers.