“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".

Szlemko admits that he is not entirely surprised by the results. “We have to remember that humans are animals too," he says. "It's unrealistic to believe that we should not be territorial.”

... “This work clearly demonstrates that people will actively defend a space or territory that they feel attached to and have personalized with markers,” Fraine says.

Szlemko suggests that this territoriality may encourage road rage because drivers are simultaneously in a private space (their car) and a public one (the road). “We think they are forgetting that the public road is not theirs, and are exhibiting territorial behaviour that normally would only be acceptable in personal space,” he says.