1. School of Traffic and Transportation, Beijing Jiaotong University, 3 Shangyuancun, Haidian District, Beijing 100044, P. R. China
2. Beijing Subway Operation Corporation, 2 Xizhimenwai Street, Xicheng District, Beijing 100035, P. R. China
3. School of Automobile And Traffic Engineering, Liaoning University of Technology, 169 Shiying, Guta District, Jinzhou Liaoning 121001, P. R. China
4. Beijing Key Laboratory of Traffic Engineering, College of Metropolitan Transportation Beijing, Beijing University of Technology, 100 Pingleyuan, Chaoyang District, Beijing 100124, P. R. China
5. Centre for Transport Studies, Imperial College London, London SW7 2AZ, UK