1. Professor, Ministry of Education (MOE), Key Laboratory for Transportation Complex Systems Theory and Technology, School of Traffic and Transportation, Beijing Jiaotong Univ., Beijing 100044, P.R. China (corresponding author).
2. Professor, Dept. of Transportation Studies, Texas Southern Univ., 3100 Cleburne Ave., Houston, TX 77004; Yangtzi River Scholar, Beijing Jiaotong Univ., Beijing 100044, P.R. China.
3. Graduate Research Assistant, Ministry of Education (MOE), Key Laboratory for Transportation Complex Systems Theory and Technology, School of Traffic and Transportation, Beijing Jiaotong Univ., Beijing 100044, P.R. China.