A complex network analysis of São Paulo rail-based urban mobility from smart-card data in 2019 and 2020

This paper analyses rail-based urban mobility in the São Paulo Metropolitan Region using anonymised smart card validations from the electronic ticketing system. We reconstruct estimated origin-destination flows from single-tap records and model the system as daily weighted mobility networks, where nodes represent stations and edges represent inferred passenger flows between stations. Classical and weighted network metrics, together with rank dynamics and community detection, are used to characterise the temporal evolution of rail mobility before and during the onset of the COVID-19 pandemic (2019-2020). The results reveal a sharp contraction and spatial reorganisation of the network in early 2020, with reduced system-wide efficiency, increased effective distances and stronger fragmentation into communities, consistent with more localised patterns and with survey-based evidence reported by the São Paulo Metro Company's (Metrô) official Origin-Destination Survey 2023. The main contributions of this paper are as follows: (i) a Transaction Sequence Number-based procedure to infer inter-station OD flows from single-tap validations; (ii) the construction of daily rail-mobility networks for 2019-2020; and (iii) a network framework to track structural changes in demand, connectivity and community structure organisation over time.