1. Postdoctoral Student, Dept. of Transportation Engineering, Ajou Univ., Suwon 442-749, Korea.
2. Professor, Dept. of Civil and Environmental Engineering, Hong Kong Polytechnic Univ., Hung Hom, Kowloon, Hong Kong (corresponding author).
3. Master Student, Dept. of Urban Planning, Univ. of California Los Angeles, Los Angeles, CA 90095-1656.
4. Professor, Dept. of Transportation Engineering, Ajou Univ., Suwon 442-749, Korea.