Some links between transport and health are widely known, such as active travel, physical (in)activity, air pollution and injuries. Others are not as apparent and are much less studied, for example social interactions. This article reviews the evidence that transport impacts on social interactions, and that social interactions impact on health. It is an updated version of part of chapter 5 from Health on the Move 2.There is growing evidence that aspects of transport influence social exclusion, social capital, social cohesion and social networks. Numerous studies have identified associations between these aspects of social interaction and morbidity and mortality. Community severance - where transport infrastructure or the speed or volume of traffic act as a physical or psychological barrier - impacts on individuals travel, social networks, and the accessibility of goods, services and facilities, and has scope to influence health through a number of routes. With the development of more comprehensive measures, such as of community severance, it is likely that there will be stronger evidence that transport influences health through these pathways.