1. Humphrey Institute of Public Affairs, University of Minnesota, 301 19th Avenue South, Minneapolis, MN 55455, USA
2. Department of Civil and Environmental Engineering and Institute of Transportation Studies, University of California, 1 Shields Avenue, Davis, CA 95616, USA
3. Department of Environmental Science and Policy and Institute of Transportation Studies, University of California, 1 Shields Avenue, Davis, CA 95616, USA