1. Institute of Transportation Studies, University of California, Davis, 1 Shields Avenue, Davis, CA 95616.
2. Institute of Transportation Engineering, Tsinghua University, 1 Qinghua Yuan, Beijing, China 100084.
3. Institute of Transportation Studies, University of California, Berkeley, 2614 Dwight Way, Berkeley, CA 94720.
4. Civil and Environmental Engineering, University of Tennessee–Knoxville, 223 Perkins Hall, Knoxville, TN 37996-2010.