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3. Beijing Government, 2016. Plan on relieving traffic congestion in Beijing. Link: 〈http://zhengwu.beijing.gov.cn/gzdt/gggs/t1431668.htm〉.
4. Beijing Transport Institute, 2015. Annual report of Beijing transport development.
5. Beijing Transport Committee, 2016. Quota of vehicle increase in Beijing in 2016. Link: 〈http://www.bjhjyd.gov.cn/jggb/201617/1452148702459_1.html〉.