This paper investigates changes in human mobility patterns in the US during the COVID-19 outbreak using real-time mobile device location data from February 2 to May 30, 2020. A Social Distancing Index (SDI) was developed to measure mobility changes at different geographic levels. The study found that both government orders and local outbreak severity significantly impacted social distancing. The SDI helps monitor real-time mobility behaviors, understand the influence of government orders, and evaluate the risk of local outbreaks.
