興建軌道交通、BRT被認為是改善城市空氣質量的一項有效舉措,但在中國缺乏經驗證據。利用斷點回歸方法,分別考察了2014—2016年全國新開通的40條軌道交通線路與24條BRT線路對空氣質量指數(AQI)的影響,結果表明:軌道交通、BRT的開通對空氣質量具有顯著且穩健的改善作用。進一步結合城市異質性、交通規模與模式特點發現:(1)當城市經濟水平較低(人均GDP<10萬)且人口規模介于100萬~500萬時,開通軌道交通或者BRT均能緩解城市空氣污染程度;當城市經濟水平較發達(人均GDP≥10萬)且人口規模介于500萬~1000萬時,開通軌道交通能顯著地降低空氣污染物濃度。(2)從交通規模效應出發,現有軌道交通的累積里程越長,新開通軌道交通線路對空氣質量的改善作用越強,而針對發揮BRT線路的環境正外部性,其里程的最優規模應保持在50~100 km范圍內。(3)不同交通模式視角,BRT_subway模式的城市其新開通軌道交通線路能顯著地改善空氣質量,但對于subway_BRT模式的城市新開通BRT線路,這并不能帶來明顯的環保效應。因此,為了避免城市盲目發展軌道交通、BRT現象的發生,二線、三線城市從投入成本考慮,選擇新建BRT不失為一項更為合理的措施;對于部分一線城市而言,新建軌道交通或者BRT均難以實現其環保效益。同時,我國的軌道交通規模尚未達到飽和狀態,政府應進一步投入資源加以完善;而BRT環境正外部性的發揮要求城市應合理規劃BRT里程建設,保證其經濟與環境雙重效益的實現。此外,對于目前同時擁有軌道交通與BRT設施的城市而言,在現有軌道交通基礎上再開通BRT線路這一決策應進行充分的評估。

The construction of rail transit and BRT are considered to be an effective measure to improve the quality of urban air,but lack empirical evidence in China. This paper adopts regression discontinuity method research the effects of the newly opened 40 rail transit lines and 24 BRT lines on the air quality index( AQI) from 2014 to 2016. These estimations prove that BRT and rail transit can significantly reduce air pollution. Moreover,through discussing the urban heterogeneity,traffic scale as well as traffic modes,this study indicates:(1)When the urban economy is low( per GDP < 10 thousand) and the population scale is between 1 and 5 million,the rail transit or BRT can improve the air quality. When the urban economic level is developed( per GDP > 10 thousand) and the population scale is from 5 to 10 million,the rail transit can significantly reduce the air pollutant concentration.(2)From the traffic scale effect,the longer the accumulated mileage of the rail transit,the stronger the effect of the newly opened route on the air quality,but the optimal scale of BRT should be kept in the range of 50 to 100 km.(3)From the perspective of different modes of transport in the city,BRT subway mode can significantly improve air quality by reopening their rail transit lines,but BRT subway mode does not lead to significant environmental benefits by reopening the BRT line. In order to avoid the blind development of urban rail transit and BRT,it’s a more reasonable measure for second-tier cities and third-tier cities to open the new BRT lines based on their costs; for large cities,the new rail transit or BRT can’t achieve environmental benefits. Meanwhile,the scale of rail transit in China has not yet reached the saturation state,and it still needs to improve the rail transit service management and infrastructure system to achieve its environmental effects. The environmental externality of BRT requires a reasonable mileage. In addition,for cities that currently have rail transit and BRT facilities,the decision on reopening BRT for improving air quality should be adequately evaluated.