[Social psychologist William] Szlemko said that, in an as-yet-unpublished experiment, he conducted tests of road rage in actual traffic.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.
Szlemko's theory is that we inhabit different kinds of private and public spaces: private (your home), semi-private or temporarily private (your work office / cubicle) and public (a park / road). Actually a road can be confusing because we're simultaneously inhabiting a private space (our car) and a public space (the road). We're hard-wired to defend our territory and people who mark their territory by personalising their cars with bumper stickers are more likely to think about their own private space than the public space they're sharing when they're on the road.
It's an interesting article.
HT: Marginal Revolution.