1. School of Transportation and Logistics, Southwest Jiaotong University, Chengdu, Sichuan 610031, China
2. Department of Mathematics and Statistical Sciences, Jackson State University, Jackson 39217, MS, USA
3. Alabama Transportation Institute, The University of Alabama, Tuscaloosa 35487, AL, USA
4. National United Engineering Laboratory of Integrated and Intelligent Transportation, Chengdu, Sichuan 610031, China