Bumper stickers speak volumes about a vehicle’s driver, but not always in the way they might hope. People who customize their cars with stickers and other adornments, no matter what they are, tend to be more prone to road rage than other people.

Road rage -- bouts of aggressive driving such as speeding or tailgating, or confrontations with other motorists -- has risen dramatically in recent years. In 1995, the American Automobile Association found 12,000 injuries and 200 deaths were linked to U.S. road rage. In 2008, the numbers are estimated to exceed 25,000 injuries and 370 deaths, and many more road rage incidents go unrecorded.

Researchers quizzed hundreds of volunteers about their cars and driving habits. Participants were asked to describe the value and condition of their cars, as well as whether they had personalized them in any way, such as with seat covers, bumper stickers, special paint jobs, stereos and even plastic dashboard toys. They also asked questions about how the participants responded to specific driving situations.

People who had a larger number of personalized items on or in their car were 16 percent more likely to engage in road rage. Only the number of bumper stickers, and not their content, predicted road rage.