1. Graduate Research Assistant, Zachry Dept. of Civil Engineering, Texas A&M Univ., 3136 TAMU, CE/TTI Building 601C, College Station, TX 77843-3136 (corresponding author.
2. Associate Research Engineer, Texas Transportation Institute, Texas A&M Univ. System, 3135 TAMU, CE/TTI Building 503B, College Station, TX 77843-3135.
3. Professor, Fred J. Benson Chair, Zachry Dept. of Civil Engineering, Texas A&M Univ., 3136 TAMU, CE/TTI Building 503A, College Station, TX 77843-3136.