1. Professor, Intelligent Transportation System Research Center, Southeast Univ., Nanjing 210096, China.
2. Research Assistant, Dept. of Civil Engineering, Tsinghua Univ., Beijing 100084, China.
3. Associated Professor, Key Laboratory of Civil Engineering Safety and Durability of China Education Ministry, Dept. of Civil Engineering, Tsinghua Univ., Beijing 100084, China (corresponding author).