Urban highways are barriers to social ties

TL;DR

This study quantifies how urban highways act as barriers to social interactions by analyzing geolocated social network data, revealing a significant negative impact on social connectivity especially in historically marginalized neighborhoods.

Contribution

Introduces the Barrier Score metric linking urban highways to social ties at individual level, providing quantitative evidence of highways' role in social segregation.

Findings

Highways are associated with decreased social connectivity.

The barrier effect is strongest for short distances.

Historical highway construction often targeted marginalized neighborhoods.

Abstract

Urban highways are common, especially in the US, making cities more car-centric. They promise the annihilation of distance but obstruct pedestrian mobility, thus playing a key role in limiting social interactions locally. Although this limiting role is widely acknowledged in urban studies, the quantitative relationship between urban highways and social ties is barely tested. Here we define a Barrier Score that relates massive, geolocated online social network data to highways in the 50 largest US cities. At the unprecedented granularity of individual social ties, we show that urban highways are associated with decreased social connectivity. This barrier effect is especially strong for short distances and consistent with historical cases of highways that were built to purposefully disrupt or isolate Black neighborhoods. By combining spatial infrastructure with social tie data, our method adds a new dimension to demographic studies of social segregation. Our study can inform reparative planning for an evidence-based reduction of spatial inequality, and more generally, support a better integration of the social fabric in urban planning.