Railway network expansion reduces air pollution in Tokyo over 25 years

We explore the long-term impact of railway infrastructure on air pollution by examining Japan’s railway network expansion over a 25-year period. Using Difference-in-Differences, regression analysis with market access, and instrumental variables strategies, we identify a causal link between railway development and improved air quality. Our findings show that railway expansion significantly reduces Suspended Particulate Matter (SPM) by 9.576$\text{\%}$ to 21.65$\text{\%}$ and Nitrogen Dioxide (${\mathrm{NO}}_2$) by 1.401$\text{\%}$ to 1.546$\text{\%}$. Results also indicate increased ridership and a shift towards railways following these expansions. Improved air quality translates to health benefits valued between 98.271 and 161.515 million USD, or approximately 1.426$\text{\%}$ to 2.342$\text{\%}$ of total construction costs. The most significant improvements are seen in areas with initially high SPM levels, with diminishing benefits noted further from central business districts. Our simulations suggest that the benefits of railway expansions will persist, advocating for continued development of railway networks as a sustainable strategy for environmental and public health enhancement.