1. School of Civil Engineering, Dept. of Transportation Engineering, Shandong Univ., Jinan 250061, China.
2. Associate Professor, School of Civil Engineering, Dept. of Transportation Engineering, Shandong Univ., Jinan 250061, China (corresponding author).
3. Lecturer, School of Civil Engineering, Dept. of Transportation Engineering, Shandong Univ., Jinan 250061, China.
4. Professor, School of Civil Engineering, Dept. of Transportation Engineering, Shandong Univ., Jinan 250061, China.