This thesis examines processes through which the barriers in the Stockholm metro are continuously rearranged. The barriers are in place with the purpose of securing income, while simultaneously enabling the flow of passengers into the metro. First, I examine the technical components and capacities of the barriers. Second, I outline a variety of actors involved with planning, manufacturing, and maintaining them, and analytically link these actors as comprising an ‘apparatus of public transport’. More specifically, this study focuses on how metro users’ practices are both influenced by, and influence how the barriers are rearranged. I show how this dynamic is enacted in the barrier milieu in metro stations, where also the tension between the purposes of securing income and allowing mobility is negotiated. The ethnographic material includes encounters with metro users, technicians, officials, and politicians in metro stations and other settings, as well as written documentations. In public discussions, the barriers are commonly at issue in relation to fare evasion. From a standpoint where technical, social, and political dimensions are understood as intermeshed, this study casts attention to a variety of practices occurring in the barrier milieu. By exploring how a technical arrangement influences social relations, I aim to raise questions of responsibility with regards to technology.