1. Research Fellow, School of Qilu Transportation, Shandong Univ., Jinan 250002, China (corresponding author). ORCID: .
2. Emeritus Professor, Dept. of Civil and Environmental Engineering, National Univ. of Singapore, Singapore 117576. ORCID: .
3. Professor, School of Qilu Transportation, Shandong Univ., Jinan 250002, China. ORCID: .