1. School of Transportation and Logistics, Southwest Jiaotong Univ., Chengdu, Sichuan 610031, China (corresponding author).
2. School of Transportation and Logistics, Southwest Jiaotong Univ., Chengdu, Sichuan 610031, China; National United Engineering Laboratory of Integrated and Intelligent Transportation, Chengdu, Sichuan 610031, China.