The effects of different travel modes and travel destinations on COVID-19 transmission in global cities

The international community has made significant efforts to flatten the COVID-19 curve, including predicting transmission [1,2], executing unprecedented global lockdowns and social dis- tancing [3,4], promoting the wearing of facemasks and social dis- tancing measures [5], and isolating confirmed cases and contacts [6]. Because of the adverse consequences of these lockdown mea- sures [7], many cities have reopened so they can rebuild their economies. However, as mobility has gradually returned towards normal, imported cases from unknown sources have disrupted the recovery situation, and cities are continually at high risk of new waves of infection [8,9] since airborne transmission is the dominant transmission route [10]. Unlike studies that focused on the effect of COVID-19 on changes in mobility [11], our study aims to determine the causative relationship and quantify the effects between travel modes and travel destinations and transmission of the pandemic, which is helpful to control the pandemic, especially during the reopening period as mobility progressively returns to normal.