Accessibility and population patterns: A study of the expansion ofthe rail network in Madrid (1998–2020)

This study examines the relationship between the expansion of the rail system in the Madrid metropolitan area and patterns of population redistribution between 1998 and 2020. We focus on two major Metro expansion phases, which together account for approximately 40% of the current network. To capture the effects of improved infrastructure, we construct an accessibility measure based on the increase in job opportunities resulting from reductions in travel time. To address potential endogeneity in this key variable, we propose an instrument based on subsoil permeability, which serves as a novel proxy for tunneling feasibility. We estimate an elasticity of population with respect to travel time of 0.7, which remains stable across varying magnitudes of travel time reductions. The effect is stronger for individuals aged 40 to 59 and for the Spanish-born population.