1. Research Engineer, Institute of Transportation Studies, Univ. of California at Berkeley, 1353 S. 46th St., Bldg. 452 (PRC), Richmond, CA 94804 (corresponding author).
2. Graduate Student Researcher, Dept. of Civil and Environmental Engineering, Univ. of California at Berkeley, 215 McLaughlin Hall, Berkeley, CA 94720.
3. Associate Professor, Dept. of Civil and Environmental Engineering, Univ. of California at Davis, 3139 Engineering III, 1 Shields Ave., Davis, CA 95616.