Since the first confirmed patient in South Korea on January 19, the mass media (e.g. TV news, newspapers, the Internet) and other studies have shown a decrease in peoples’ engagement in outdoor activities as a result of self-isolation, working from home, voluntarily staying indoors, delaying the commencement of schools and universities, and the delivery of educational messages for COVID-19 prevention (e.g. via the Internet, broadcast media, and written articles) (Chinazzi et al., 2020, Magal and Webb, 2020). Similarly, our study showed that, following the COVID-19 outbreak in South Korea, nationwide traffic decreased by 9.7% compared with 2019, indicating a decrease in citizens’ outdoor activities. In particular, after the KCDC raised the infectious disease alert level to ‘orange’ on January 27, a large decrease was observed in nationwide traffic. After the alert level was raised to ‘red’ on February 22, traffic in the fourth week of February was down by 26.1% compared with 2019 (Figure 4).