1. Lecturer, School of Transportation Science and Engineering, Beijing Univ. of Aeronautics and Astronautics, No. 37 Xueyuan Rd., Haidian District, Beijing 100191, China (corresponding author).
2. School of Transportation Science and Engineering, Beijing Univ. of Aeronautics and Astronautics, No. 37 Xueyuan Rd., Haidian District, Beijing 100191, China.