1. Graduate Research Assistant, Dept. of Transportation, Southeast Univ., Sipailou 2, Nanjing, Jiangsu 210008, China (corresponding author).
2. Professor, Dept. of Transportation, Southeast Univ., Sipailou 2, Nanjing, Jiangsu 210008, China.
3. Professor, Dept. of Civil and Environmental Engineering, 301N Patton Hall, Virginia Tech, Blacksburg, VA 24061.
4. Associate Professor, Dept. of Transportation, Southeast Univ., Sipailou 2, Nanjing, Jiangsu 210008, China.