1. Assistant Research Scientist, Texas Transportation Institute, The Texas A&M Univ. System, College Station, TX 77843-3135 (corresponding author).
2. Assistant Professor, Zachry Dept. of Civil Engineering, Texas A&M Univ., College Station, TX 77843-3135.
3. Professor, Zachry Dept. of Civil Engineering, Texas A&M Univ., College Station, TX 77843-3135.