1. Research Scientist, Virginia Tech Transportation Institute, 3500 Transportation Research Plaza, Blacksburg, VA 24061-0536 (corresponding author).
2. Founder’s Professor of Engineering, Dept. of Civil Engineering and Environmental Engineering, 205 N. Mathews Ave., Univ. of Illinois at Urbana-Champaign, Urbana, IL 61801.
3. Assistant Professor, Dept. of Civil Engineering and Construction, 1501 West Bradley Ave., Peoria, IL 61625.