1. Ab Initio, Lexington, MA.
2. Professor, Dept. of Civil and Environmental Engineering, Carnegie Mellon Univ., Pittsburgh, PA 15213-3890.
3. Director, Urban Transportation Center, Univ. of Illinois-Chicago, Chicago, IL 60607.
4. Research Assistant, Dept. of Civil and Environmental Engineering, Carnegie Mellon Univ., Pittsburgh, PA 15213-3890.