The Effect of Metro Expansions on Air Pollution in Delhi
研究了德里地铁扩建对三种交通源污染物（一氧化碳、二氧化氮、PM2.5）的短期影响，发现一氧化碳在主要交通路口下降34%，二氧化氮也有下降趋势，但PM2.5数据缺失结论不明确。
The Delhi Metro (DM) is a mass rapid transit system serving the National Capital Region of India. It is also the world's first rail project to earn carbon credits under the Clean Development Mechanism of the United Nations for reductions in CO2 emissions. We analyze whether the DM led to localized reduction in three transportation source pollutants. Looking at the period 2004–2006, one of the larger rail extensions of the DM led to a 34 percent reduction in localized CO at a major traffic intersection in the city. Results for NO2 are also suggestive of a decline, while those for PM2.5 are inconclusive due to missing data. These impacts of pollutant reductions are for the short run. A complete accounting of all long run costs and benefits should be done before building capital intensive metro rail projects.