The Frontal Cortex

When I first got a Prius, I was tempted to cover the rear bumper with liberal decals, like "Support Local Farms!" (that's on my bike) or "Women for Obama!" (a popular Prius sticker here in New Hampshire). I wanted to embrace my inner cliche, to see what it felt like to be a right-wing talking point. (I also enjoy the occasional latte...) But then, just as I was about the deface the car with ideological mottos, my better half intervened. She had no interest in being a cliche.

As usual, my better half was right: it turns out that putting bumper stickers on your car increases your aggressive tendencies as a driver. When you cover the vehicle with marks of identity, you become more sensitive to "invasions of territory," which apparently include being cut off by another car:

Watch out for cars with bumper stickers.

That's the surprising conclusion of a recent study by Colorado State University social psychologist William Szlemko. Drivers of cars with bumper stickers, window decals, personalized license plates and other "territorial markers" not only get mad when someone cuts in their lane or is slow to respond to a changed traffic light, but they are far more likely than those who do not personalize their cars to use their vehicles to express rage -- by honking, tailgating and other aggressive behavior.

It does not seem to matter whether the messages on the stickers are about peace and love -- "Visualize World Peace," "My Kid Is an Honor Student" -- or angry and in your face -- "Don't Mess With Texas," "My Kid Beat Up Your Honor Student."

Drivers who do not personalize their cars get angry, too, Szlemko and his colleagues concluded in a paper they recently published in the Journal of Applied Social Psychology, but they don't act out their anger. They fume, mentally call the other driver a jerk, and move on.

"The more markers a car has, the more aggressively the person tends to drive when provoked," Szlemko said. "Just the presence of territory markers predicts the tendency to be an aggressive driver."