Paul Atchley, an associate professor of psychology at the University of Kansas, conducted research this year and last to determine whether young adults had enough self-control to postpone responding to a text message if they were offered a reward to do so. The idea was to determine whether the lure of the device was so compelling that it would override a larger reward.

The research found that young adults would postpone the text. Dr. Atchley concluded that the phone, while not classically addictive, nevertheless has a powerful draw, in part because it delivers information that often becomes less valuable with each passing minute.

“What looks like an addiction, in my opinion, based on this data, is a reflection of the fact that information loses value over time very rapidly,” he said. “If people can make choices, it’s not addiction.”

The first study of drivers texting inside their vehicles shows that the risk sharply exceeds previous estimates based on laboratory research — and far surpasses the dangers of other driving distractions.

The new study, which entailed outfitting the cabs of long-haul trucks with video cameras over 18 months, found that when the drivers texted, their collision risk was 23 times greater than when not texting.

In 2003, researchers at a federal agency proposed a long-term study of 10,000 drivers to assess the safety risk posed by cellphone use behind the wheel.

They sought the study based on evidence that such multitasking was a serious and growing threat on America’s roadways.

But such an ambitious study never happened. And the researchers’ agency, the National Highway Traffic Safety Administration, decided not to make public hundreds of pages of research and warnings about the use of phones by drivers — in part, officials say, because of concerns about angering Congress.

But does chatting to passengers have the same detrimental effect on driving? An earlier study found that it does not. That research, led by Frank Drews of the University of Utah, analysed the performance of young drivers using a vehicle simulator. Dr Drews found that when using a hands-free phone, a volunteer “drove” significantly worse than he did when just talking to someone playing the role of a passenger. Passengers, the researchers believed, might even help road safety by commenting on surrounding traffic.

The reported does not seem to have distinguished between idle chatter with people in the car and serious conversation.   But I could see notices going up warning people against serious conversations in person or on the phone, while in a car.