1. Ph.D. Candidate, Dept. of Civil and Environmental Engineering, Carnegie Mellon Univ., 5000 Forbes Ave., Pittsburgh, PA 15213.
2. Graduate Student, Dept. of Civil and Environmental Engineering, Univ. of California-Berkeley, 760 Davis Hall, Berkeley, CA 94720.
3. Professor, Dept. of Civil and Environmental Engineering, Carnegie Mellon Univ., 5000 Forbes Ave., Pittsburgh, PA 15213.
4. Associate Professor, Depts. of Civil and Environmental Engineering and Engineering and Public Policy, Carnegie Mellon Univ., 5000 Forbes Ave., Pittsburgh, PA 15213 (corresponding author).
5. Professor and Head, Dept. of Civil and Environmental Engineering, Carnegie Mellon Univ., 5000 Forbes Ave., Pittsburgh, PA 15213.