1. Researcher, Virginia Tech Dept. of Civil and Environmental Engineering, Virginia Polytechnic Institute and State Univ., Blacksburg, VA 24061 (corresponding author).
2. Senior Research Associate, Center for Sustainable Transportation Infrastructure, Virginia Tech Transportation Institute, Blacksburg, VA 24061.
3. Director, Center for Sustainable Transportation Infrastructure, Virginia Polytechnic Institute and State Univ., Blacksburg, VA 24061.