1. Lecturer, School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081, China; Institute for Transport Studies, Univ. of Leeds, Leeds LS2 9JT, U.K. (corresponding author).
2. Assistant Professor, Key Laboratory of Regional Sustainable Development Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing 100101, China; Institute for Transport Studies, Univ. of Leeds, Leeds LS2 9JT, U.K.
3. Professor, School of Traffic and Transportation Engineering, Central South Univ., Changsha 410075, China.
4. Professor, School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081, China.