“Repulsive interactions between pedestrians” aren’t just dirty looks among people vying for the same spot in the crosswalk.

They’re one of several scientifically measurable forces that quietly guide the way pedestrians forge trails across lawns in parks, campuses and other open areas.

In the latest issue of the journal Nature, scientists from Clark Atlanta University in Georgia and two institutes in Germany merge physics with human behavior to come up with a method that one day may help urban planners design the most comfortable and convenient paths.

Building on the observation that people often form their own paths instead of sticking to the main drags, the scientists tried to figure out what influences where people walk.

Comparison of computer models to real-life trails showed that a balance between two factors was important. Pedestrians weighed how directly a trail took them to their destination and how well-established the trail was.

Incorporating other factors into the model also might help planners with walkways other than outdoor trails, said Peter Molnar of Clark Atlanta University.

Those repulsive pedestrian interactions - science-speak for people’s innate desire not to run into each other - influences walkers’ behaviors in crowds, he said. The number of the pedestrians and their sense of personal space could affect how broad an airport corridor should be built, for instance.

The new model might also have a wider scientific impact because it describes a phenomenon known as a self-organized system, Molnar said. In such a system, a group of individuals, without talking to one another or receiving instructions, can create patterns from nothing.