1. Grad. Res. Asst., School of Civ. Engrg., Purdue Univ., West Lafayette, IN 47907. E-mail: enelson@ecn.purdue.edu
2. Assoc. Prof., School of Civ. Engrg., Purdue Univ., West Lafayette, IN 47907 (corresponding author). E-mail: darcy@purdue.edu
3. Asst. Dir., Texas Transp. Inst., Texas A&M Univ., College Station, TX 77843. E-mail: t-urbanik@tamu.edu