This article aims to study the construction process of the subway system in the Brazilian cities of Salvador and Lauro de Freitas, investigating the constraints of state agencies to build this subway infrastructure. By examining the structures created to produce this urban infrastructure policy, this paper tries to explain how institutional arrangements of public policies condition state agency, in other words, how they enhance or undermine the formation of policy capacities to deliver subway infrastructure. The qualitative analysis of the data suggests that the design of institutional arrangements and their change influence the availability and mobilization of actors, resources, competences and policy instruments towards the promotion of efficacy and legitimacy in this policy.