1. School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore
2. School of Transportation, Jilin University, Changchun 130022, P. R. China
3. School of Traffic and Transportation, Beijing Jiaotong University, Beijing 100044, P. R. China
4. School of Automotive and Transportation Engineering, Hefei University of Technology, Hefei 230009, P. R. China