Air quality impacts of new public transport provision: A causal analysis of the Jubilee Line Extension in London. (15th January 2021)

• Record Type: Journal Article
• Authors: Ma, Liang; Graham, Daniel J.; Stettler, Marc E.J.
• Is Part Of: Atmospheric environment. Volume 245(2021)
• Publication Date: 2021-01-15
• Subjects: Air quality -- Public transport -- Causal analysis -- Regression discontinuity design -- Gradient boosting decision trees -- Change point detection; Air -- Pollution -- Periodicals; Air -- Pollution -- Meteorological aspects -- Periodicals; 551.51
• DOI: 10.1016/j.atmosenv.2020.118025
• Languages: English
• ISSNs: 1352-2310

Abstract

Abstract: Public transport is commonly associated with benefits such as reducing road traffic congestion and improving air quality. This paper focuses on evaluating the causal impact of a new public transport provision in London, the Jubilee Line Extension (JLE) in 1999, on air quality. Using meteorological normalisation and a regression discontinuity design with time as the forcing variable, we show that the JLE led to only small changes in air pollution at some specific locations; detectable changes in NOx, NO2, and O3 concentrations were found at 63%, 43% and 29% of air pollution monitoring sites, respectively. For those sites where a change in pollution was detected, the responses ranged from −2% to +1% for NO2 and -1% to 0% for O3 . We calculate that the long-run effects are greater, ranging from −11% to +3% for NO2 and from −2% to +2% for O3 at sites that showed a response to the JLE. Aggregating across all sites in London for a city-wide effect, both short and long-run effects were less than 1% or insignificant. We find statistically significant increases in NO2 and O3 concentrations at some background sites, but the magnitude of effect is within +1% in the short-run and +3% in the long-run. Our analysis shows that the effect of the JLE on air pollution in some areas was greater than others, however across London the effect was small and this indicates that public transport provision on its own is not an effective strategy to improve air quality. Highlights: An increase in public transport supply did not improve air quality at all sites. Public transport provision on its own is not effective to improve air quality. Short-run changes in pollution concentrations ranged from −2% to +1%. Long-run changes in pollution concentrations may range from −11% to +3%.