Railways to better minds: The influence of high-speed rail on cognitive health inequalities

Cognitive impairment has become a major challenge to health aging all over the world, and evidence shows that transportation infrastructure affects the elderly's cognitive health. However, little is known about the effects of high-speed rail (HSR) on cognitive health. Based on the panel data from 2011 to 2018, this study employs the double machine learning (ML) approach to examine the relationship between HSR and cognitive health among 11,572 middle-aged and aged adults in China. The result shows that the opening of HSR significantly improved global cognition, with an estimated treatment effect coefficient of 0.198 (95 % confidence interval, [0.088, 0.309]). The effect of HSR varies in dimensions of cognitive health, only promoting mental intactness rather than episodic memory. The main result remains robust after conducting a series of robustness tests such as introducing instrumental variables, replacing the HSR measurements and ML method. Further analysis shows that HSR has heterogeneous effects on cognitive health across gender, ages, education levels, rural-urban areas, and geographic regions. For instance, HSR has narrowed the cognitive health inequalities between individuals with elementary or middle school education and those with higher education, but widened the gap between rural and urban residents. Additionally, mediation analysis indicates that HSR may enhance cognitive health by reducing PM2.5 exposure, improving individual earnings, and alleviating depressive symptoms. This study provides beneficial insights for China and other countries to develop transportation infrastructure and promote healthy cognitive aging.