1. Institute of Transportation Studies, University of California−Davis, Davis, California 95616-7384, United States
2. Economic Research Service, US Department of Agriculture, Washington, DC 20250-0002, United States
3. Center for Global Trade Analysis, Department
of Agricultural Economics, Purdue University, West Lafayette, Indiana 47907-2056, United States
4. Goldman School of Public Policy, University of California−Berkeley, Berkeley, California 94720, United States