<p>We innovatively shift the research focus from traditional metro systems to the broader spectrum of urban rail transit systems to study the relationship between rail transit development and urban pollution. Previous studies have predominantly concentrated on metro systems, often overlooking the various forms of rail transit such as light rail, trams, and commuter trains, each with distinct environmental impacts. By broadening the scope to include these diverse modes, our research offers a comprehensive analysis of how urban rail transit systems contribute to pollution reduction in Chinese cities. Utilizing panel data from 2011 to 2023, we investigate the effects of rail transit development on air quality, focusing on two primary mechanisms: replacing taxi usage and lowering per capita traffic energy consumption. Our empirical findings, derived from a Difference-in-Differences approach, reveal that the expansion of urban rail transit significantly reduces urban pollution levels. Additionally, we identify variations in effectiveness across different city sizes and regions, with larger cities and eastern regions experiencing more pronounced benefits. These insights underscore the importance of tailoring urban rail policies to local contexts. The study concludes with policy recommendations aimed at maximizing the environmental benefits of urban rail transit systems.</p>