Mitigator or generator? A systematic review of how public transport shapes social segregation

Public transport is increasingly recognised as a contributing factor of social segregation, yet empirical evidence presents a mixed picture regarding its role. Through a PRISMA-guided systematic review of 30 studies (2008–2025), this paper synthesises evidence on how transit interventions shape segregation outcomes along two organising pathways: a behavioural pathway, through which transit is associated with expanded mobility and opportunities for diverse social encounters; and a structural pathway, through which transit-induced land-use changes reshape neighbourhood composition. Findings reveal that transit is generally associated with reductions in activity-space segregation, yet its relationship with residential segregation is heterogeneous, often accompanied by gentrification and displacement. Importantly, gains in cross-group exposure measured by activity-space indices can come with hidden costs: displaced lower-income residents often face longer commutes and greater time-poverty, which may limit the quality of social contact even as mobility-based mixing increases. We also identify methodological challenges – including endogeneity, the modifiable area unit problem, and the assumption that mobility-based co-presence reflects social interaction. The findings suggest that the social effects of transit access are shaped by operational features such as service frequency, fare structures, and network topology. Building on this synthesis, we identify priorities for future research, including longitudinal person-based tracking, stronger causal identification strategies, and richer accessibility models that capture a wider range of mobility costs. Together, these advances would help clarify the conditions under which transit investment supports more equitable urban outcomes.