UC Merced

UC Merced study shows urban rail reduces carbon monoxide air pollution

The opening of a major urban rail system in Taiwan caused a meaningful reduction in air pollution, according to a study by two UC Merced professors. "Despite the importance of the transportation sector for air pollution, little work has examined the air pollution effects of transportation infrastructure directly," Professor Alexander Whalley and Professor Yihsu Chen wrote in the paper. The UC Merced study, called "Green Infrastructure: The Effects of Urban Rail Transit on Air Quality," helps to answer a long-debated question about whether investment in urban rail transit helps improve air quality by taking cars off the road. The study has been accepted for publication in the "American Economic Journal: Economic Policy."

Whalley is an economist at UC Merced and Chen is a professor of environmental and energy economics. The Taipei Metro opened in 1996 as a new urban rail transit system, the culmination of an effort to improve the city's transportation and air quality. From the 1970s to the 1990s, Taipei had some of the worst air among the world's largest cities, with a significant amount coming from automobiles. Whalley and Chen used hourly air quality data from Taiwan to quantify how the new rail transit system impacted the air quality. There have been two schools of thought when it comes to the impact of rail transit infrastructure: Some argue that a large and well-run system decreases air pollution by encouraging people to take the train rather than a car, while others say investing in infrastructure increases people’s likelihood for traveling, reducing any benefits. The UC Merced researchers found that the system’s opening caused a 5-to-15-percent reduction of carbon monoxide. They also found some evidence that there was a reduction in the nitrogen oxides in the air. The public health impacts implied in the findings are an important beneficial aspect of mass transit infrastructure often not taken into account by policy makers, according to the study. The rail transit system, however, had little detectable impact on ground-level ozone, which is indirectly related to automobile emissions. Whalley and Chen also found little evidence suggesting that automobile travelers adjusted their time or route of because of the availability of rail transit.