1. School of Qilu Transportation, Shandong University, Jinan, Shandong, China;
2. Department of Civil and Environmental Engineering, University of Nevada, Reno, Reno, NV, USA;
3. Department of Civil, Environmental, and Construction Engineering, Texas Tech University, Lubbock, TX, USA;
4. School of Traffic and Transportation, Lanzhou Jiaotong University, Lanzhou, Gansu, China