1. Dept. of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea.
2. Ph.D. Student, Dept. of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea.
3. Professor, Dept. of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea (corresponding author).
4. Doctor, Expressway and Transportation Research Institute, Hwaseong, Gyonggi 445-812, Korea.