1. Ph.D. Student, School of Transportation Science and Engineering, Beihang Univ., 37 Xueyuan Rd., Beijing 100191, China (corresponding author).
2. Professor, School of Transportation Science and Engineering, Beihang Univ., 37 Xueyuan Rd., Beijing 100191, China.
3. Senior Engineer, China Railway Siyuan Survey and Design Group Co, Ltd, Wuhan 430063, China.