City Streets Are Shifting From Social Hubs to Throughways

A study, led by Arianna Salazar-Miranda, assistant professor of urban planning and data science at the Yale School of the Environment, analyzed recorded pedestrian behavior in New York City, Boston, and Philadelphia using AI. The research team measured walking speed, group sizes, group formation, and lingering behaviors exhibited in videos from 1979-1980 and 2008-2010 and found that average walking speed has increased by 15%, while pedestrians now spend half the amount of time lingering than they did in the late 1970s. The frequency of group encounters also declined; there is less spontaneous interaction; and public spaces are dominated by single individuals. The study, published in PNAS, highlights a changing urban dynamic that has important implications for the role of public spaces in society.

“The findings push us to think not just about whether public spaces are accessible, but whether they are serving their broader civic function,” said Salazar-Miranda, who directs the Livable City Lab at YSE.

The team’s research builds on the work of William Whyte, who studied street life in urban settings for the New York City Planning Commission and manually coded hours of video with a team of students. With the use of AI, Salazar-Miranda’s team, which included scientists from MIT’s Senseable City Lab and Harvard, reviewed Whyte’s video footage from 1979-1980 archived by the Project for Public Spaces, as well as footage from 2008-2010 taken by Michigan State University Professor Keith Hampton. In their analysis, they were able to revisit questions about human behavior in urban settings and quantify changes.

“This study shows how AI could turn people-watching into a precise science, uncovering hidden patterns and proposing useful solutions to make our cities work better,"  said Carlo Ratti, professor at the MIT Senseable City Lab and senior author on the study.  "Deployed correctly, this inhuman technology could be a powerful tool to help make our cities more humane."

There are several possible reasons for the changes in pedestrian behaviors, the study authors note. Significant increases in urban incomes may be leading to a greater demand for speed as time has become more valuable. The proliferation of cafes and indoor spaces may also be leading to less time lingering on city streets. Smart phones also may play a role in changing urban behavior.  Also, as people pay more attention to their phones, they are less likely to seek out or participating in social encounters on the street. However, the prevalence of smart phones alone doesn’t fully account for the decline, the authors said.

“The study lays the groundwork for more research into why these shifts are happening — what role do things like income, smartphone use, or indoor amenities play? And how can design intervene?” Salazar-Miranda said.