# **_1. Introduction_**

The COVID-19 pandemic significantly affected lifestyle and mobility worldwide, ranging from a dramatic decrease in travel to an unprecedented increase in teleworking. These impacts resulted from governmental measures, with some affecting whole sectors in the economy, and some affecting crucial infrastructure sectors, such as transport. After the outbreak of COVID-19, the local governments of many cities have suspended the operations of buses and subways to prevent people from being infected with COVID-19, reducing the gathering of crowds, and required new safety standards, including requirements to wear masks. These measures implied a major reduction in service capacity compared to the pre-COVID-19 era, by affecting ridership due to a dramatic decrease in travel demand levels as well as imposing regulations that have consequences for service capacity. Such restrictions have significantly affected people's mobility behavior, with individual choices to refrain from traveling in order to reduce exposure and risk of contamination.

One of the sectors that has experienced a major impact is transportation, which is the focus of this paper. Urban travel has declined all over the world, but not uniformly for all modes; public transportation has taken the hardest blow, as shown by survey-based data (Molloy _et al.,_ 2020; Astroza _et al.,_ 2020, Tirachini and Cats, 2020). As a result, there has been a widespread reduction in public transport ridership: according to recent estimates, passenger numbers in cities around the world have been at the peak of the pandemic down 70% to 90% (Google, 2020). Much of the changes in travel demand has been attributed to individuals' adjustments in their daily travel activities such as replacing out-of-home activities with in-home activities. The impact of COVID-19 on public transport varies depending on the stage of the coronavirus spread. The loss of public transport demand can mostly be attributed to reduced travel demand resulting from a combination of public health restrictions, working from home, online schooling, shift to online shopping, transit service cuts, and loss of employment and fear of infection (HoneyRos ́es _et al.,_ 2020; De Vos, 2020).

The sharp reduction in public transportation demand due to the new physical distance behaviors and the fear of COVID-19 contagion challenges the future sustainability of mobility in cities. This is because in some cases the reduction in services has been accompanied by a reduced service supply and exacerbated by the perception of public transportation as riskier than private or personal means of transport because of the closer contact to other people that is possible, sometimes unavoidable, in public transportation vehicles and stations. Since the beginning of the pandemic, most public transport operators have quickly stepped up and taken concrete action to make transit systems COVID-safe for staff and passengers. But despite the best efforts of professionals across the sector, the COVID-19 crisis has dealt a massive blow to public transport. The economic and social effects of the COVID-19 outbreak in public transportation extend beyond service performance and health risks to sustainable mobility. However, little is known regarding individuals' immediate response in terms of adjusting their travel activities.

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