1. Assistant Professor, Dept. of Civil Engineering, Univ. of Nebraska, Lincoln, NB 68588-0531 (corresponding author).
2. Graduate Research Assistant, Dept. of Civil Engineering, Univ. of Nebraska, Lincoln, NB 68588-0531.
3. Associate Research Scientist, Texas Transportation Institute, College Station, TX 77843-3135.
4. Professor, Dept. of Civil Engineering, Texas A & M Univ., College Station, TX 77843-3135.