1. Professor, Key Laboratory of Rd. and Traffic Engineering of the Ministry of Education, Tongji Univ., Shanghai 201804, CN, (Corresponding author), e-mail: fpxiao@gmail.com
2. Professor, Department of Civil Engineering, Univ. of Alabama, Tuscaloosa, AL 35487, US.
3. Associate Professor, Highway School, Chang'an Univ., Xi'an 710064, CN.
4. Assistant Professor, Dept. of Civil and Environmental Engineering, Rutgers, The State Univ. of New Jersey, New Brunswick, NJ, 08901, US.