1. Associate Research Fellow, Upper Great Plain Transportation Institute, North Dakota State Univ., NDSU Dept. 2880 P. O. Box 6050 Fargo, ND 58108-6050 (corresponding author).
2. Director, Upper Great Plain Transportation Institute, North Dakota State Univ., NDSU Dept. 2880 P. O. Box 6050 Fargo, ND 58108-6050.