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In policy remedies, transportation infrastructure such as metro transit is widely considered to be an important and effective means to reduce air pollution. However, the policy prediction that metro transits reduce air pollution depends on driver responses. China provides an appropriate context to explore the answer since its major cities have expanded their metro transit systems in recent years, which enables us to exploit a natural experiment. Accordingly, a sharp regression discontinuity is employed to evaluate the impact of 112 metro lines (with an accumulation of 3286 km) on air quality. Evidence shows that the opening of metro transits has a negative causal effect on air pollution. The results are robust to several alternative specifications. Furthermore, a heterogeneity analysis demonstrates that metro openings have a time-varying impact on air pollution, which is larger during rush hours. We anticipate that the air quality improvement in China caused by metro transits can generate large welfare gains. [ABSTRACT FROM AUTHOR]

Emissions from heavy urban traffic have been the most abundant components of urban air pollution in China. Compared to the fast increasing consumption of automobile, the growth rate of urban traffic infrastructure investment (UTII) is relative low. It is a controversial issue for the policymaker whether promoting the UTII could make a positive impact on reducing air pollution or not. This study is designed to test the relations between the UTII and air quality, using the data of 83 cities from 2000 to 2012. Based on the empirical results from the fixed effect model and dynamic panel data model, increasing the UTII could generally mitigate the air pollution, but the long-run and short-run effects are significantly different. In the short run, the UTII effect on air quality is −0.02, since the urban traffic infrastructure construction might cause more detours and road blockages, which would enhance the fine-particle emissions of the low-speed traffic. In contrast, the UTII could widen the roads and make the traffic system more accessible in the long run, so the estimated positive effect is about 0.05. The robustness tests about different regions and scales of cities are conducted. Policy suggestions are further recommended to reduce air pollution. [ABSTRACT FROM AUTHOR]

Traffic-related air pollution has become an urgent problem in many developing countries with rapid industrialization and urbanization. Traffic infrastructure construction, especially road reconstruction, is a prominent instrument of improving the road capacity and then affecting air quality. We employ the road area as the proxy variable of road infrastructure construction and further divide the road reconstruction pattern into lengthening pattern and widening pattern, respectively to evaluate the impact on urban air quality. The empirical result shows that the coefficient of road infrastructure construction represented by the road area is between −0.0818 and −0.0905, which means increasing road area has an emission-alleviating effect on air pollution. Moreover, we also find that the effect of road lengthening on air quality is better than road widening in the eastern China, but the improvement of road widening in the Central and Western China is better than the road lengthening. The result provides a valuable reference for policy recommendations on urban road infrastructure planning to improve air quality. • An empirical study is conducted to explore the effect of road construction. • Air pollution index is selected as the dependent variable to measure urban air quality. • An increase in road area can improve air quality. • Two road construction methods both have air pollution-reducing effect. • In the eastern cities, road lengthening is more effective in improving air quality. [ABSTRACT FROM AUTHOR]