We spotted unusual bright lights and drove to investigate. It came towards our vehicle as if it were going to hit us.A friend and I saw a bright figure from about 4 miles away and we decided to take that route on the interstate to see what it was. When we began crossing the Grand Marsh bridge over the Missouri River, we saw this large object somewhat hovering over the river. My cellular phone failed to function at this time. There were bright white lights completely around it and there was one green light. The one green light made the object look almost triangular in shape, but It could have been spherical. The top of it was slightly rounded and the bottom was flat. As we went further across the river, the object started to come towards our vehicle. It continued to come towards our vehicle and then the next thing we knew, it was going the opposite direction. The only time it moved quite fast was when we began to follow it, other than that, it moved quite slow and steady. We followed the object for about 2 minutes afterwards and lost it over a hill in Bismarck, North Dakota.