Transportation policies have an important incidence on the allocation of resources within cities. Therefore, investigating the impacts of transit investment is relevant especially in developing countries where informal housing is highly prevalent and spatial disparities are remarkable. We study the impact of a transit expansion of the Metrocable system in Medellín (Colombia) as a natural scenario to understand the causal links between lowering access cost and informal housing. Using a difference-in-difference identification strategy, we estimate that the expasion of Line H of Metrocable reduces informal housing up to 15 percentage points. We also show that the magnitude of the effect depends on the distance to the intervention. When exploring potential mechanisms mediating the analyzed causal relation we find that the labor market plays a crucial role.