.:: Green Transportation :: Subways ::

Exploring how subways affect people's travel mode choice and air pollution


Public transit is viewed as a potential means to mitigate traffic
congestion and its resulting air pollution and health consequences. 

.:: Examining Two Cities ::

Beijing, one of China's most motorized cities, experienced an average annual increase of 11.8% in the number of motor vehicles from 2000-2010.

How will the development of subways affect automobility (car ownership and usage) of residents? 

Recently, Changsha experienced rapid increases in vehicle ownership, with 1.29 million privately-owned vehicles in 2014, resulting in severe traffic congestion and air pollution. 

Are areas close to subway services experiencing more improvement in air quality than areas further away from subway lines within the same city? 

.:: Beijing ::Subways + Car Ownership ::


We examine the impact of subway station proximity on urban residents’ car ownership and fuel consumption.


A 2009 household survey (826 households) conducted by Tsinghua University in Beijing reveals that car ownership rate in the sample is 47%. We also see that households living closer to a subway station are less likely to own a car.

Subway proximity reduces a household’s probability of owning a car and subsequent fuel consumption.


The effect of subway on car ownership is stronger where subway provides a shorter time to travel to the city center.
This suggests that more convenient subway stations discourage nearby households’ car ownership more.

.:: Changsha :: Subways + Air

Quality ::


We examine the effect of the city’s first subway line (Line No. 2; opened April 2014)

on local air pollution.


Using hourly air quality data (10 monitoring stations) from Jan 2013 to April 2015, we compared the difference in air quality pre- and post opening of Changsha's subway Line No.2.

The opening of the subway line substantially reduced nearby CO emissions by 18.1% compared to areas further away

Reduction effects for air pollution are significantly larger during rush hour, subway operation hours and weekdays.


This suggests that the introduction of the subway line encouraged people to switch from 
private cars to public transit, resulting in fewer cars on the road and an improvement in air quality.

.:: When investing in public transit, 
social benefits (congestion + air pollution mitigation)
should be considered along with matching investment 
with transit-oriented development
s ::



Web and Visuals

Siqi Zheng
MIT China Future City Lab, Department of Urban Studies and Planning, 
Center for Real Estate

Xiaonan Zhang
Tsinghua University

Weizeng Sun
Jinan University

Jianghao Wang
Chinese Academy of Sciences

Yingjie Zhang
Beijing Forestry University

Cong Sun
Shanghai University of Economics and Finance

Rui Wang
Johns Hopkins University, UCLA

Siqi Zheng, Xiaonan Zhang, Weizeng Sun and Jianghao Wang. “The effect of a new subway line on local air quality: A case study in Changsha, Transportation Research Part D: Transport and Environment. 2018.

Yingjie Zhang, Siqi Zheng, Cong Sun and Rui Wang. “Does Subway Proximity Discourage Automobility? Evidence from Beijing, Transportation Research Part D: Transport and Environment. 2017, 52: 506-517.

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The material on this website can be used freely. We just ask that it is duly credited as a project by MIT China Future City Lab, and a PDF is sent to cfclab@mit.edu.