1. Professor, Dept. of Civil and Environmental Engineering, Utah State Univ., Logan, UT 84322-4110 (corresponding author).
2. Transportation Engineer, Bureau of Planning, Dept. of Highways, Bangkok 10400, Thailand.
3. Graduate Student, Dept. of Civil and Environmental Engineering, Utah State Univ., Logan, UT 84322-4110.
4. Professor, Dept. of Civil Engineering, The Univ. of Hong Kong, Pokfulam Road, Hong Kong, China.