You don't need a car to get road rage.

For many people, few things are more infuriating than slow walkers—those seemingly inconsiderate people who clog up sidewalks, grocery aisles and airport hallways while others fume behind them.

Researchers say the concept of "sidewalk rage" is real. One scientist has even developed a Pedestrian Aggressiveness Syndrome Scale to map out how people express their fury. At its most extreme, sidewalk rage can signal a psychiatric condition known as "intermittent explosive disorder," researchers say. On Facebook, there's a group called "I Secretly Want to Punch Slow Walking People in the Back of the Head" that boasts nearly 15,000 members.

Some researchers are even studying the dynamics that trigger such rage and why some people remain calm in hopes of improving anger-management treatments and gaining insights into how emotions influence decision making, attention and self control.

"We're trying to understand what makes people angry, what that experience is like," says Jerry Deffenbacher, a professor at Colorado State University who studies anger and road rage. "For those for whom anger is a personal problem, we're trying to develop and evaluate ways of helping them."