1. Graduate Research Assistant, Texas Transportation Institute, Texas A&M Univ., CE/TTI Building Office 501G, 3135 TAMU, College Station, TX 77843-3135 (corresponding author).
2. E.B. Snead I Associate Professor, Zachry Dept. of Civil Engineering and Texas Transportation Institute, Texas A&M Univ., 3135 TAMU, College Station, TX 77843-3135.
3. Assistant Professor, Dept. of Civil, Architectural and Environmental Engineering, Univ. of Texas at Austin, 1 University Station, C1761, Austin, TX 78712-0278.
4. Professor, Dept. of Civil Engineering and Texas Transportation Institute, Texas A&M Univ., 3135 TAMU, College Station, TX 77843-3135.