More cars clog the streets while sprawling roads creep outward, and the pressure to hurry from point A to B climbs.

Frustrations begin to simmer, and aggressive driving?even violent road rage?can boil over.

Though numbers are hard to find, anecdotal evidence suggests road rage is on the rise. University of Utah researchers are looking into the physical and psychological responses to stressful driving conditions.

The situation itself is part of the problem. Automobile travel is an antisocial experience for drivers, not a natural situation for humans beings, said Dave Strayer, an associate professor in psychology.

“We didn’t evolve to live in a high density, anonymous society,” Strayer said. On the road, other drivers become nameless obstacles to a goal.

“How often are you happy when there are other people on the freeway?” he asked.

In Utah, the situation is not improving. The 2000 census found more commuters and slightly longer drive times. More than 19,000 Utah households had five or more cars.

Participants in a study navigated a simulated freeway complete with accidents, weaving cars and stop-and-go traffic.

The idea behind the study is that several factors must come together for road rage to occur?difficult driving conditions, time stress and a psychological profile that tends to act aggressively, Strayer said.

In addition to blood pressure, heart rate and other physiological measurements, subjects filled out a questionnaire to provide psychological information.

Moderate, or even difficult, driving simulations had little effect on the subjects’ blood pressure.

“Stop-and-go traffic doesn’t have to be stressful,” said Timothy Smith, professor and chairman of the psychology department. “It’s the frame of mind that’s important.”

Add an incentive to hurry, and the situation can change entirely.

However, the additional stress of driving under a time limit may be linked to road rage, Strayer said.

The situation is analogous to competing with other drivers in an attempt to find parking and still get to class on time, he said.

Preliminary results from the freeway simulation show a time limit induced a physical stress response associated with road rage?but only in the male subjects.

Both men and women were offered a $5 incentive if they could reach a destination more quickly than half the other study participants.

The blood pressure of the male subjects increased by 10 percent when they hurried. Meanwhile, female subjects under the same conditions showed negligible response to the same scenario.

The male and female difference has many potential explanations. Perhaps gender roles encourage men to act more competitively than women. Perhaps video games have conditioned men’s responses, Smith suggested. Perhaps women have a higher threshold for this sort of pressure.

Regardless, the gender difference came as a surprise. In other studies, women and men have show similar responses to incentive-based scenarios such as being paid to deliver a good speech.

Elevated blood pressure and heart rate are part of the body’s stress response. Though the stress of driving is psychological, the body responds as if there is physical work to do?increasing blood flow.

The same physiological response has also been associated with heart disease, Smith said.

The gender difference uncovered by the study is just the tip of the iceberg, researchers expect to have more detailed research in several months.

Bert Uchino, an associate professor of psychology, and Frank Drews, a post-doctoral researcher, also contributed to the study.