Outdoor social distancing behaviors changed during a pandemic: A longitudinal analysis using street view imagery

Abstract

Social distancing, defined as maintaining a minimum interpersonal distance (often 6 ft or 1.83 m), is a non-pharmaceutical intervention to reduce infectious disease transmission. While numerous quantitative studies have examined people's social distancing behaviors using mobile phone data, large-scale quantitative analyses of adherence to suggested minimum interpersonal distances are lacking. We analyzed pedestrians' social distancing behaviors of using 3 years of street view imagery collected in a metropolitan city (Seattle, WA, USA) during the COVID-19 pandemic. We employed computer vision techniques to locate pedestrians in images, and a geometry-based algorithm to estimate physical distance between them. Our results indicate that social distancing behaviors correlated with key factors such as vaccine availability, seasonality, and local socioeconomic data. We also identified behavioral differences at various points of interest within the city (e.g., parks, schools, faith-based organizations, museums). This work represents a first of its kind longitudinal study of outdoor social distancing behaviors using computer vision. Our findings provide key insights for policymakers to understand and mitigate infectious disease transmission risks in outdoor environments.

Fig 1. Sample output of the pedestrian detection and social distance estimation algorithm.

There are 2 pedestrians, with an estimated 14.38 ft between them. Additional sample images are available in the S1 File.

Fig 2. Summary data from the outdoor social distancing analysis.

The blue line represents the number of distances under 9 ft (2.74 m) per image. For example, 1.0 means that there is one pair of pedestrians on average per image, whose distance is under 9 ft.

Fig 3. Cumulative vaccination totals over time in King County, Washington, where Seattle is the largest city, show diminishing willingness to get vaccines.

Data collected from the King County Department of Public Health [40].

Fig 4. The left side graph shows the death rates per 100,000 citizens for different racial groups in King County, WA [47].

(NHPI, Native Hawaiian or Pacific Islander; AIAN, American Indian or Alaska Native). The right side graph shows the expected proportion of distances under 9 ft per image across our entire data set during the summer, in a lower-income census tract, on a weekday, before the vaccine became publicly available, based on our regression results. It is shown here that the more white areas did not have a statistically significant difference from the less white areas.