1. Ph.D. Student, School of Transportation and Logistics, Southwest Jiaotong Univ., 999 Xi’an Rd., Xipu Town, Pidu District, Chengdu, Sichuan 611756, China (corresponding author).
2. Professor, School of Transportation and Logistics, Southwest Jiaotong Univ., 999 Xi’an Rd., Xipu Town, Pidu District, Chengdu, Sichuan 611756, China.