According to a 2006 study by the National Highway Traffic Safety Administration and the Virginia Tech Transportation Institute, inattentive drivers, which include those on cell phones, account for 80 percent of crashes and 65 percent of near crashes.

A study released by the Texas Transportation Institute said that half of Texas high school students surveyed said they frequently speak on the phone while they drive, and about 40 percent read or send text messages while they're behind the wheel.

The latest, most visible, and most controversial source of driver in-attention is the handheld cell phone. For many motorists, to see another driver talking on the phone is to see red. Cell phones have been available for 20 years and are now everywhere—the Cellular Telecommunications & Internet Association says there are 137 million subscribers in the United States. Cell phone use by drivers has become very common: According to NHTSA, at any given moment of the day, 500,000 drivers of passenger vehicles are talking on handheld cell phones.

This adds up to a lot of miles driven by people who are not necessarily giving their full attention to driving. And handheld phones aren't the only culprit: The AAA Foundation for Traffic Safety has found that use of hands-free phones also contributes to inattention.

Legislation to address the perceived hazard of cell phone use behind the wheel has been passed in many places. Australia, Austria, Germany, Greece, Ireland, Italy, Japan, Russia, and Switzerland have all restricted cell phone use by drivers.

In the United States, bills to restrict cell phone use in cars have been introduced in both the House and the Senate. Among the states, only New York has passed a law banning the use of handheld cell phones for drivers, although other states are considering similar laws. In California, Nevada, and Utah, bills to ban cell phone use while driving have failed.