城市轨道交通减排治污效应评估

Assessment of emission reduction effect of urban rail transit

兴建轨道交通成为城市扩张过程中减排治污的重要举措。由于缺乏系统数据以及样本选择导致的内生性偏误,使得系统的跨城市估计轨道交通减排治污效应的文献相对匮乏。而系统评估轨道交通的外部性,对改进和优化线路规划、站点设置以及网络布局,具有重要意义。本文利用断点回归(RD)评估了从2015年10月到2018年9月期间,全国省会城市新增线路对空气污染的治理效应,以此检验轨道交通的减排治污效果。回归结果表明:①新增轨道交通对空气质量(AQI)的治理并不显著,但却能使PM 2.5降低20.03%,PM 10降低20.46%。②人口规模会对轨道交通的减排效果产生异质性影响,常驻人口不足600万时,新增轨道交通能减少17%~29%的机动车尾气污染;人口规模在1200~1500万时,对机动车尾气的减排治污效果在24%~77%之间不等,减排效果最明显。③随着线路数量的增加,轨道交通减排的规模效应递减。城市新增至第三条轨道交通线路时,减排治污效应最为明显;超过第7条之后,新增线路不再存在减排治污的规模效应,治理作用难以奏效。④减排治污的规模效应集中在累积里程数达到50~100 km以及每百万常住人口累积通车里程达到3~5 km,其余累积里程难以实现减排治污的项目初衷。⑤进一步分析表明,交通创造效应和交通分流效应是新增轨道交通减排效应呈现异质性的原因,也是导致减排治污规模效应递减的原因。本文的政策启示是,利用兴建轨道交通来实现减排治污效果须因地制宜,并非规划和开通越多线路,就越有利于改善城市空气质量,要以提升交通的分流效应为前提。

The construction of rail transit has become an important measure to reduce pollution in the process of urban expansion.Due to the lack of systematic data and endogenous errors in sample selection,there is a relative lack of systematic and cross-city literature on estimating the emission reduction and pollution control effects of rail transit,while systematic investigating externalities of the rail transit system is of great significance for improving and optimizing the route planning,site setting and network layout.The aim of this paper is to investigate the impact of openings of rail transit lines on air pollution reduction in the provincial capital cities from October 2015 to September 2018,by employing the regression discontinuity analysis(RD).Our results show that:①openings of the new rail transit lines in this period does not significantly improve air quality,but it makes PM 2.5 of the city reduce by 20.03 percent,and PM 10 reduce by 20.46 percent.②The emission reduction and pollutants control effects of new lines have heterogeneous effects among cities with different resident size.When the size is less than 6 million,openings of the new rail transit can reduce the emission of motor vehicle exhaust pollutants by 17 percent to 29 percent.While the size is between 12 million and 15 million,the emission reduction effects vary from 24 percent to 77 percent.③With the increase of the number of lines,the scale benefit of the emission reduction effect of rail transit decreases.When the new rail transit line is added to the third line,the effect of pollution reduction and pollution control is the most obvious.After exceeding the 7th line,there is no scale effect anymore,and the effect of pollution reduction and pollution control is difficult to be effective in statistics.④the scale effect concentrates on the aggregate mileage of 50~100 km and 3 to 5 km per million residents,elsewise it is difficult to achieve the original intention of emission reduction and pollution control targets.⑤Further analysis shows that traffic creation effect and traffic diversion effect are the causes of heterogeneity of emission reduction effect of new lines,and also the causes of decreasing scale effect of emission reduction and pollution control.The policy enlightenment of this paper is that the use of rail transit to achieve emission reduction and pollution control targets must be adapted to local conditions,not planning and opening more lines,the more conducive to improving urban air quality.It is necessary to enhance the traffic diversion effect as the premise for achieving emission reduction targets.