I am a truck driver and was traveling south on hwy 81, after turning east on hwy 46, I noticed something in front of me--maybe 200 ft off the ground traveling south bound very slowly, but very very large,there were no visable lights an ther was no noise that I could hear. It was foggy in layers and in and out of my veiw. It was metallic in color. It was so large I could not see how tall it was. I could veiw I think the bottom portion of the object. I could see the curve 0f the bottom only. As it travled south I could see it was extremely long, maybe the length of a football field. When I first saw it I was probably 1/2 to 3/4 mile from the object. By the time I reached it It had already crossed the hwy and my headlights were no longer able to light the object. I was very curious about it and tried to speed towards it as fast as I could. But could not get close enough fast enough to get a better view. Almost looked like the bottom half of a 747 jet liner. After the object was out of sight was when reality hit me and I did get very frightened of what I saw. I proceeded east to the first truck stop which was outside of Beresford, South Dakota where I stopped and went inside. I inqired at the fuel desk if anyone had reported anything in the sky. The man looked at me as if I was crazy as I told him what I had seen. I was physically shaken.This was 19 years ago and this is the first time I have reported this incident to anyone. I also have 3 photos of a UFO my sister found in an antique store that she stopped at in Winner,South Dakota. She inspected a dresser and an taped to the underside of one of the drawers was several pictures of a UFO. There were no dates on these pictures,but looked to be from the 50's or 60's. She gave me only 3 pictures, which I still have today.