According to a new report from the California Highway Patrol, reported on by the San Jose Mercury- News in this article, cellular phone use is the leading cause of car accidents that are due to driver distraction.
Further, in the past week, researchers in Utah have determined that speaking on a cellular phone, regardless of whether the speaker is using a hands-free headset, is more distracting than speaking to a person next to you in the car.
Both of these reports, considered together, do beg for some further study.
The California study has garnered a lot of press, because of the sensational numbers, but it is important to remember that less than 10% of all accidents in California are considered to be caused by driver distraction, and about 20% of those are "caused" by cellular phones, making them responsible for about 2% of the crashes, much less than excessive speed, etc.
The Utah report, described in a CNN article on Monday, states that cellular phones are more distracting than talking to a person in the car next to you. In particular, the reasoning is that somebody else in the car will slow down the conversation or stop talking when a situation gets more complex, whereas the person on the other end of the cellular phone can't see the traffic and won't do so. They also state that the cellular distraction is the same with and without handsfree. Note: this study was also reported in August, when it was originally published.
A more detailed press release from the University of Utah details the study, which included 110 students, of which 3 hit a simulated car when talking on a cellular phone, whereas the control group did not strike the car.
Frankly, I was a bit suprised by both sets of claims in Utah, since in my experience, the use of hands-free devices substantially increases awareness and alertness and I have found that people tend to turn their heads (thus letting their eyes leave the road) when speaking with people in the car.
I'd like to see a larger study done on this, and one wherein the set-up involves testing the control and the cell-phone groups against unexepected road activity during the highway driving or less stressful driving conditions.