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%–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 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.

中文翻译：

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新公共交通设施对空气质量的影响：对伦敦银禧线延长线的因果分析

摘要 公共交通通常具有减少道路交通拥堵和改善空气质量等好处。本文重点评估了 1999 年伦敦新公共交通设施（Jubilee Line Extension (JLE)）对空气质量的因果影响。使用气象归一化和以时间为强制变量的回归不连续性设计，我们表明 JLE 仅导致某些特定位置的空气污染发生很小的变化；分别在 63%、43% 和 29% 的空气污染监测点发现了 NOx、NO2 和 O3 浓度的可检测变化。对于那些检测到污染变化的地点，NO2 的响应范围为 -2% 到 +1%，O3 的响应范围为 -1%–0%。我们计算出长期影响更大，在显示对 JLE 有反应的地点，NO2 的范围从 -11% 到 +3%，O3 的范围从 -2% 到 +2%。汇总伦敦所有地点的全市影响，短期和长期影响均小于 1% 或不显着。我们发现某些背景地点的 NO2 和 O3 浓度在统计上显着增加，但影响的幅度在短期内在 +1% 以内，在长期内则在 +3% 以内。我们的分析表明，JLE 对某些地区空气污染的影响大于其他地区，但在整个伦敦，影响很小，这表明公共交通提供本身并不是改善空气质量的有效策略。我们发现某些背景站点的 NO2 和 O3 浓度在统计上显着增加，但影响的幅度在短期内在 +1% 以内，在长期内则在 +3% 以内。我们的分析表明，JLE 对某些地区空气污染的影响比其他地区大，但在整个伦敦，影响很小，这表明公共交通提供本身并不是改善空气质量的有效策略。我们发现某些背景站点的 NO2 和 O3 浓度在统计上显着增加，但影响的幅度在短期内在 +1% 以内，在长期内则在 +3% 以内。我们的分析表明，JLE 对某些地区空气污染的影响大于其他地区，但在整个伦敦，影响很小，这表明公共交通提供本身并不是改善空气质量的有效策略。