Lots of people get mad behind the wheel, but who are the people likely to try and kill you at the intersection? A CSU psychologist found that road rage correlates with large numbers of bumper stickers:

Szlemko and his colleagues 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.

The researchers recorded whether people had added 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.

To keep the participants from realizing that the team was collecting information about aggressive driving, questions such as "If someone is driving slow in the fast lane, how angry does this make you?" were interspersed with decoy questions such as "What kind of music do you listen to in the car?". Szlemko's team used a pre-existing scale called "Use of vehicle to express anger" to diagnose the presence of road rage in their participants.

People who had a larger number of personalized items on or in their car were 16% more likely to engage in road rage, the researchers report in the journal Applied Social Psychology.

"The number of territory markers predicted road rage better than vehicle value, condition or any of the things that we normally associate with aggressive driving," say Szlemko. What's more, only the number of bumper stickers, and not their content, predicted road rage -- so "Jesus saves" may be just as worrying to fellow drivers as "Don't mess with Texas".

The paper is here.
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The part about it being irrelevant to bumper sticker content is pretty interesting. Apparently all the people with the "Make Love, Not War" bumper stickers in Boulder aren't immune to this impulse.

The authors attribute the anger caused by driving as the conflict between the personal space of your car and the public space of the road. To assert your personal space, you have territorial markings like bumper stickers. Those who more forcefully assert their space are more likely to be enraged by the conflict.

More at the Washington Post.'

Hat-tip: Slashdot