1. School of Traffic and Transportation, Lanzhou Jiaotong University, Lanzhou, Gansu 730070, China
2. Key Laboratory of Road Traffic Engineering of the Ministry of Education, Changsha University of Science and Technology, Changsha, Hunan 410114, China
3. Hunan Provincial Key Laboratory of Intelligent Processing of Big Data on Transportation, Changsha University of Science and Technology, Changsha, Hunan 410114, China
4. Department of Civil Engineering, City College of New York, NY 10031, USA