Exploring dual-directional collective human mobility vulnerability and the built environment in places: Lessons from the COVID-19 pandemic

Place-level human mobility reflects the collective movement patterns of individuals and groups within defined geographic areas for specific mobility patterns. The COVID-19 pandemic has underscored the pressing concerns on mobility vulnerability during urban crisis. While socioeconomic disparities in mobility disruptions have been thoroughly documented, the impact of the built environment during the pandemic remains inadequately explored. Moreover, the vulnerability of collective human mobility in specific places, considering dual-directional patterns of both incoming and outgoing behaviors, is not well understood. This study utilizes extensive mobile phone data to investigate human mobility vulnerability across U.S. cities at the census block group (CBG) level during COVID-19, focusing on both incoming and outgoing mobility patterns. By integrating socioeconomic and built environment factors, we aim to identify the determinants that influence place-level mobility vulnerability in response to the pandemic. We assess year-over-year disparities in bidirectional mobility density, dwell time, and distance between 2019 and 2020 to evaluate their vulnerabilities in CBGs. The results reveal significant roles of built environment variables on the vulnerability and robustness of various mobility patterns. Our findings underscore the pronounced advantages and drawbacks of the built environments such as developed open space, retail density, employment diversity, job-worker balance, walkability, and transit service frequency on specific patterns of incoming and outgoing mobility vulnerability. Furthermore, interventions in the built environment aimed at promoting sustainable mobility should also consider the potential threats associated with mobility vulnerability. These insights provide practical implications for post-pandemic planning initiatives designed to enhance resilience. © 2025 Hong Kong Society for Transportation Studies