Urban Rail Network and Local Air Quality in Shenzhen: Focusing on the Mediating Role of Network Density and Scale in the Traffic-diversion Effects

Abstract

<p>We examine the air-quality effects of urban-rail development in Shenzhen, taking a difference-in-differences approach. Our results demonstrate that the effects of urban rail on local air quality largely vary by time, depending on network density and scale. New station openings in Shenzhen had no significant impacts on local air quality or even worsened it until the 2010 metro-line extension, when the city’s metro network density was still low, with limited spatial service coverage. However, urban rail functioned as a significant pollution abator after the 2016 extension as the network grew denser and more comprehensive. The rail-driven anti-pollution effects tended to be further strengthened with externalities arising from improved network connectivity, spilling over the effects beyond newly opened stations to preexisting ones. Shenzhen’s case also shows substantial spatial heterogeneity, in that new metro stations in proximity to neighborhoods that share key characteristics in transit-oriented development generate a greater anti-pollution effect.</p>