PHOTO: Eric Hood/iStockphoto

5 June 2008—Human beings are creatures of habit, and new data shows that we may be less spontaneous than previously thought. In a study detailed this week in the journal Nature, researchers from Northeastern University, in Boston, used cellphone signals to demonstrate that human travel patterns are similar among individuals and conform to a simple mathematical model.

“We were surprised by some of the aspects of the study,” says lead author Marta González. “There is a lot of similarity between the behavior of people.”

The study analyzed human motion by monitoring cellphone records and tracking each phone’s signal as it moved from one phone tower to the next. They used the data to come up with a probability equation for describing human movement. The results could have implications for urban planning, traffic monitoring, and the spread of disease, all of which rely on human travel.

This is not the first study to try to quantify human travel. In 2006, researchers from the Max-Planck-Institute for Dynamics and Self-Organization, in Göttingen, Germany, tracked the movement of dollar bills. As with this recent study, their data also fit into a mathematical model. But the German model could make predictions only about groups of people; it could not say anything about individual human travel. That’s because dollar bills frequently change hands. Cellphones, on the other hand, usually stay with one person, so the researchers were able to track the movements of individuals.

“In comparison to our dollar bill study, it’s a step ahead,” says Dirk Brockmann, lead author of the Max Planck study and also an associate professor of engineering sciences and applied mathematics at Northwestern University, in Evanston, Ill.

The researchers from Northeastern University obtained cellphone records from 100 000 anonymous users and tracked the data over six months. The time, date, and location of the base station receiving each call or text message was tracked, allowing the researchers to reconstruct the route of the user. Then they calculated the distances between each call.

The results showed that during the six months of the study most people traveled very short distances most of the time, while some traveled great distances. Ninety-four percent of the people traveled less than 100 kilometers, while only 0.2 percent traveled more than 500 kilometers. Short trips, naturally, were more frequent than long ones. The study also found that all users, despite the number of trips or distance traveled, visited a couple of places frequently—probably their home and their workplace.