1. Professor, School of Transportation Science and Engineering, Harbin Institute of Technology, Harbin 150090, P.R. China (corresponding author).
2. Ph.D. Student, School of Transportation Science and Engineering, Harbin Institute of Technology, Harbin 150090, P.R. China.
3. Associate Professor, Dept. of Civil and Environmental Engineering, Rutgers, State Univ. of New Jersey, New Brunswick, NJ 08854.
4. Engineer, Dept. of Road Engineering, Jilin Provincial Transportation Planning and Design Institute, Changchun 130021, P.R. China.