Easy subway access predicts the resilience of New Yorkers' friendships

In Social Connectedness in Urban Areas (Sci-Hub mirror), a group of business and public policy researchers from Facebook, NYU and Princeton study anonymized, fine-grained location data from Facebook users who did not disable their location history, and find that the likelihood that New Yorkers will remain friends is well correlated with the ease of commuting between their respective homes on public transit.

The negative effect of distance on friendships is both intuitive and validated through empirical research, but the paper finds that the effect size for longer commutes is much more pronounced than mere distance: while a 10% increase in distance correlates to a 10% decrease in a reduction in Facebook friendship, a 10% increase in commute times correlates to a 15% reduction in friendships.

For now, the researchers haven't done work to suggest that the relationship between friendship and public transportation travel time holds for places outside of New York City. And it's true that in the US, New York is sui generis—no other city has such a well-developed and widely used transit system. But researchers think it's possible that transportation determines "friendships" elsewhere, too. "I think if you did this for a city that's not New York, public transit wouldn't matter, but road routings would matter," says Leah Brooks, an economist at George Washington University who has studied cities and transportation systems. It's very possible, she says, that two neighboring suburban areas might not have a lot of social connections if there's not an easy way to get between them. Brooks' own research has found that cities continue to be shaped by long-ago public transit infrastructure, like streetcar lines. "If you told me public transit matters [to social connectedness] in San Diego, I'd be really surprised," she says—the city doesn't have great transit.

Social Connectedness in Urban Areas (Sci-Hub mirror [Michael Bailey, Patrick Farrell, Theresa Kuchler and Johannes Stroebel/NBER]

In New York, Friendships Run Along Subway Lines [Aarian Marshall/Wired]