1. Vis. Asst. Prof., Dept. of Civ. Engrg., Carnegie Mellon Univ., Pittsburgh, PA 15213‐3890
2. Formerly, Asst. Prof., Transp. Systems Div., Dept. of Civ. Engrg., Massachusetts Inst. of Tech., Cambridge, MA 02139
3. Res. Asst., Transp. Systems Div., Dept. of Civ. Engrg., Massachusetts Inst. of Tech., Cambridge, MA
4. Res. Asst., Dept. of Comput. Sci., Univ. of California, Berkeley, CA 94720