Accessibility and population patterns: A study of the expansion of the 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 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. • Madrid’s 1998–2020 metro expansion significantly boosted suburban residential growth: a 10% reduction in travel time to jobs is associated with a 7% increase in population. • Improved accessibility reinforced agglomeration near stations, particularly for Spanish-born residents, supporting suburbanization patterns consistent with evidence from other European cities like Paris and Barcelona. • To address endogeneity, we use a novel instrument—subsoil permeability—as a proxy for tunneling feasibility, highly relevant since about 78% of the metro system (and most of the expansion) was built underground. • The effects are heterogeneous: strongest for Spanish-born residents and those aged 40–59, with little or no relocation among foreign-born or older residents.