1. Research Assistant, Dept. of Civil and Environmental Engineering, Carnegie Mellon Univ., 5000 Forbes Ave., Pittsburgh, PA 15213; presently, Transportation Systems Engineer, Booz Allen Hamilton, 20 M St. SE Washington, DC 20003 (corresponding author).
2. Hamerschlag University Professor of Engineering Emeritus, Dept. of Civil and Environmental Engineering, Carnegie Mellon Univ., 5000 Forbes Ave., Pittsburgh, PA 15213.
3. Assistant Professor, Dept. of Civil and Environmental Engineering, Carnegie Mellon Univ., 5000 Forbes Ave., Pittsburgh, PA 15213.