Looking to Avoid Aggressive Drivers? Check Those Bumpers.

Researchers in Colorado say drivers with stickers and decals are far more likely to use their vehicles to express rage. (By Justin Sullivan -- Associated Press)

Previous research has shown that these different territorial spaces evoke distinct emotional responses. People are willing to physically defend private territory in ways they would never do with public territory. And people personalize private territory with various kinds of markers -- in their homes, for example, they hang paintings, alter the decor and carry out renovations.

"Territoriality is hard-wired into our ancestors from tens of thousands of years ago," said Paul Bell, a co-author of the study at Colorado State. "Animals are territorial because it had survival value. If you could keep others away from your hunting groups, you had more game to spear . . . it becomes part of the biology."

Drivers who individualize their cars using bumper stickers, window decals and personalized license plates, the researchers hypothesized, see their cars in the same way as they see their homes and bedrooms -- as deeply personal space, or primary territory.

Unlike any environment our evolutionary ancestors might have confronted, driving a car simultaneously places people in both private territory -- their cars -- and public territory -- the road. Drivers who personalize their cars with bumper stickers and other markers of private territory, the researchers argue, forget when they are on the road that they are in public territory because the immediate cues surrounding them tell them that they are in a deeply private space.

"If you are in a vehicle that you identify as a primary territory, you would defend that against other people whom you perceive as being disrespectful of your space," Bell added. "What you ignore is that you are on a public roadway -- you lose sight of the fact you are in a public area and you don't own the road."

Szlemko said that, in an as-yet-unpublished experiment, he conducted tests of road rage in actual traffic. He had one researcher sit in a car in a left-turn lane. When the light turned green, the researcher simply stayed still, blocking the car behind.

Another researcher, meanwhile, examined whether the blocked car had bumper stickers and other markers of territoriality. The experimental question was how long it would take for the driver of the blocked car to honk in frustration.

Szlemko said that drivers of cars with decals, bumper stickers and personalized license plates honked at the offending vehicle nearly two full seconds faster than drivers of cars without any territorial markers.