First, we thought it was Venus, next we thought it was a large jet with it's landing lights on...now, we don't have a clue.At approximately 1745 hrs on 12/13/02, we were driving due west on I-80, 70 miles west of Salt Lake City. I was looking at a bright light out almost due west and a little bit north. I told my friend, "Hey, look how bright Venus is there." I continued to look at it due to it's beauty and brightness. In seconds, it was very obvious it was not Venus, and it wqas coming directly into us, getting bigger and brighter. My friend said, "that isn't Venus, it's a plane with it's landing lights on." The closest large airport was 70 miles East, however. However, it continued getting bigger, brighter, and closer until it was obvious it wasn't your typical plane, for sure. By then, it was getting extremely close and bright, coming directly overhead. At it's closest, I could actually make out individual lights on the front of the object, there were many, emitting bright light, with a touch of blue. The individual lights were round in shape, evenly spaced, on the front of what looked like a delta-wing object. I had the impression that it was extremely large, the exact shape and dimensions of it were tough to see due to the brightness of the lights. There were no strobes, no colored lights, no landing lights, etc...it wasn't like any aircraft I had ever seen. Although we were on a dangerous part of the freeway, noted for wrecks, I wish we would have stopped and gotten out of the car in the emergency lane to get a better look at this thing, whatever the hell it was. There were no reference points, so we could not determine the size or altitude of this, the speed appeared quite fast...it looked like the description of the Phoenix lights I have seen, that's the closest description I have.