My daughter and I were traveling to Goodlettsville from Gallatin between 4:00 and 4:30 pm. We were just about to get on Vietnam Vets Parkway. I had noticed a couple of aircraft in the sky. Both of them were leaving a contrail as they went through the sky that very quickly disappeared behind them. It was generally clear; the only clouds I noticed were at the horizon where the sun was setting. Just as I was about to approach Vietnam Vet's, I slowed down for a traffic light. I happened to glance up, and noticed a metallic object quickly going by. It was at my 11 o'clock position, traveling from NE to SW. Just as I saw it, the sun glinted off of it, and then it simply vanished. Since I was at a stop at the light, I had time to really look for it, but it was nowhere to be seen. There were absolutely no clouds up there that it could have gone behind. I remember thinking as I first saw it that it was strange that it was not leaving a contrail, as the other planes were. I could not judge the altitude, but it looked like it was considerably lower than the planes were. It looked bigger than the planes I had seen, so I'm assuming it was lower. It did look spherical, but of course, right as I noticed it the light reflected off of it, so I could not say for sure that it was. I know I didn't notice any wings. After it disappeared, I tried to make sense of what I saw, and thought that just maybe I had seen a plane. Then I happened to see a real plane as it was making approach to the Nashville airport. I could see the wings and everything, even though it was many miles away, and the object I had seen was almost directly overhead. I realized that 1) if that had been a plane that I had seen that was just too low to leave a contrail, I would have seen the wings, and 2) the reflection flash happened on the opposite side of the craft from the setting sun.((NUFORC Note: Witness elects to remain totally anonymous; provides no contact information. PD))