People in moving cars have been talking to one another for over 100 years, and, apart from a few jokes about it, no one seemed to notice or care. Now that there is sometimes a cell phone interposed between the talkers, concern about the resulting distraction to the driver has caused many government authorities to outlaw or consider outlawing talking on a cell phone while driving. At least two studies indicate cell phones increase the chance of a crash by close to 400%. http://www.cnn.com/2005/US/07/12/cells.drivers/index.html

Is it true that talking on a cell phone is more distracting for a driver than talking to his passenger, and, if so, why is it so?

Now, we may know why because of some experiments done in Japan by Takashi Hamada and colleagues at the National Institute of Advanced Industrial Science and Technology.

Their findings are as follows: "While a car is moving, the strength of signal received by a driver's phone continually changes, and the phone often has to switch from one base station to another during a call. That causes a slight loss of sound quality, forcing the driver's brain to work harder to work out what the person at the other end is saying. Hamada's team measured the sound quality of mobile phone calls in parked cars and in cars traveling at 65 kilometers per hour. A comparison of the two types of voice signal revealed silent periods of about 300 milliseconds interrupting the signal roughly six times a minute. They also discovered a time lag of about 300 milliseconds for a phone in a moving car, while for 5 per cent of the time, the frequency range becomes distorted.

The researchers then played 11 volunteers an audio recording of a story that included similar interruptions. As the volunteers struggled to hear the distorted parts of the recording, their right parietal cortex, the part of the brain that perceives sound, became more active (Transport Research Part F, DOI: 10.1016/j.trf.2005.04.016)."

Previously, it was generally assumed that speaking to passengers was less distracting, because they would stop talking when they perceived that the driver needs to concentrate. While this may remain part of the explanation, it appears that a bigger problem is that speech from cell phones in a moving car is of poor quality and this forces the listener to concentrate harder in order to understand the words. Almost by definition, the more the more a driver needs to concentrate on something other than driving, the more distracted he becomes. It requires more concentration to understand speech from a cell phone than speech from a passenger's mouth.

The cell phone system is notoriously bad in the U.S. compared to other countries, and one consequence is that the bad sound quality leads to distraction and accidents. This suggests that cell phone buyers should overweight the sound and reception quality when judging what cell phone to buy.

Still, the widespread media coverage of this issue probably gives a false impression of reality. Despite the fact that over 85 percent of the 100 million+ cell-phone subscribers regularly talk on the phone while driving, according to a survey by Prevention Magazine, there has not been a spike upwards in accident rates. Since cell phones became common in the United States, accidents as measured by fatalities have increased slightly from 40,716 in 1994 to 42,643 in 2003, and that increase is less than the increase in population, number of cars, or total miles driven. Adjusted for total number of miles driven, fatality rates due to automobile accidents continue their decades-long trend downwards.

http://www-fars.nhtsa.dot.gov/

There are many causes of accidents other than driver distraction. Distraction caused between 17 and 50 percent of accidents, depending on how distraction is defined and on whose numbers one accepts. Among distraction accidents, cell phones are but one of many distracting devices, such as radios and CD players, in cars. Passengers, eating food, roadside emergencies, looking at scenery, and reading are other distractions known to cause accidents. Many years ago I noticed a spike in accidents in the summer along Lake Shore Drive in Chicago at the stretch where the road runs right next to a beach.