People who are using headsets to talk on cell phones hands-free behind the wheel take significantly longer to detect and react to changes while driving, new research suggests.

As a result, it may not be safe for drivers to talk on the phone even when they keep both hands on the wheel, study author Dr. Arthur F. Kramer told Reuters Health.

“Should you talk on a hands-free cell phone when driving? No. It’s a risk,” he said.

Kramer explained that previous research has suggested that using a hands-free phone while driving is no safer than holding a phone to your ear. To investigate further, Kramer and his team asked 14 young drivers (average age of 21) with at least one year of driving experience and 14 older drivers (average age of 68) to have a casual hands-free conversation with someone in another room while watching a windshield-sized screen.

The screen contained images of Chicago traffic, which would sometimes quickly switch to the same scene with an added element, such as a child running into a driver’s path. As soon as the study subjects noticed a change, they pressed a button and said what it was.

When young drivers completed the task, they reacted more slowly to crucial changes when they talked on the phone, and even missed some crucial changes.

And when older drivers watched the screen, they detected meaningful changes like a child in danger, but not more quickly than they saw changes that had no impact on driving safety, such as an irrelevant advertisement, the authors report in the journal Human Factors.

“We really want drivers to detect the little girl before the thing on the side of the road,” Kramer said.

Kramer, who is based at the University of Illinois at Urbana-Champaign, said that, despite their extra experience, older drivers may be slower to react to changes because of age-related changes in the brain.

Even a slight change in reaction time can have major consequences behind the wheel, Kramer noted. “Several seconds can be a lot when you’re driving,” he pointed out.

In contrast, when drivers simply listened to a conversation between two people and said nothing - as if they were listening to talk radio - they reacted to changes at the same speed as if there were no conversation at all.

Kramer said that some people have argued that a hands-free cell-phone conversation is equivalent to talking to a car passenger, and that if you ban one type of conversation, you should have to ban the other - a prospect that doesn’t seem very likely.

In fact, Kramer and his colleagues are currently investigating the impact of talking to car passengers on driving. However, he believes that because passengers can react to what is going on around a driver and modify their conversation when there is danger, such conversations are probably not equivalent to hands-free phone conversations. “It could be very different talking to a person who can see what you’re seeing,” he said.

SOURCE: Human Factors, Fall 2004.