Interaction of travel time and transfer frequency in trip chains affected by contagion impedance during COVID-19 in Seoul

COVID-19 instilled a fear of contagion and altered the travel behaviour of public transport (PT) users. Unlike car travel, PT users are in close proximity to many individuals. Efforts to prevent the spread of contagion and ensure the safety of PT users necessitate an understanding of the factors influenced by fear that lead to behavioural changes. Building on existing research regarding the behavioural aspects of PT route choice, this paper posits that PT users adjusted their travel times and transfer frequencies to minimize exposure to contagion. Understanding these adjusted travel times and transfer frequencies is more straightforward than calculating the marginal disutilities associated with in-vehicle travel time and transfer frequency, which is the primary focus of most impedance research in transportation science. The study aims to investigate how PT users modified their travel times and transfer frequencies in response to COVID-19. Specifically, this paper develops new measures of behavioural response: Contagion Impedance (CI) and Contagion Impedance Strength (CIS). These measures indicate how travel time and transfer frequency interact in response to the spread of contagion and the intensity of that interaction. The study analyses individual trip records obtained from smartcard data of PT users in Seoul, comparing data from before and after the COVID-19 outbreak. The analysis revealed that trip chains exhibited reduced travel times and increased transfer frequencies following the significant spread of contagion. This suggests that the fear of contagion while on board was more pronounced than the fear experienced during transfers. Furthermore, the intensity of the interaction increases as the severity of contagion spread intensifies. Additional analyses segmented by age and time of day revealed distinct patterns in the interaction and its intensity. The results clearly indicate that the relationships between in-vehicle travel time and transfer time during a contagious disease differ from those in ordinary situations.