1. Associate Transportation Researcher, Texas Transportation Institute, Texas A&M Univ., 601D CE/TTI Building, College Station, TX 77843-3136 (corresponding author).
2. Professor, Dept. of Civil Engineering, Texas A&M Univ., 503A CE/TTI Building, College Station, TX 77843-3136.
3. Research Engineer, Texas Transportation Institute, Texas A&M Univ., 508E CE/TTI Building, College Station, TX 77843-3136.