Sphere over Riverton, WY

The report, as filed

I was by myself driving from Shoshoni to Riverton. The sun had gone down a couple hours earlier and it was cloudy, so it was a very dark night. The roads were icy so my attention was very firmly on the road. Out of the corner of my eye I saw a light to the right of my car. I turned my head and looked at it. About 20 feet to the right of my car was a glowing sphere. It was about the size of a basketball. It shifted colors every few seconds going from green to red to yellow. The light coming off of it wasn't extremely bright, but in the darkness, it stood out clearly. The sphere was going exactly the same speed as my car. I was driving under the speed limit because of the icy road. I was going about 45 mph. I kept looking over at it and it stayed in the same position relative to my car outside the driver's (sic. passenger's) side window. The ground dropped off sharply a few feet beyond the guardrail. My first thought was that there must be a parallel road down below and another vehicle that happened to be going the exact same speed as myself had a tall pole attached to it with a weird color changing light on top of it. As strange as that would be it was the only explanation I could come up with. After 15 or 20 seconds of this sphere matching my speed and direction perfectly it was becoming clear to me that my initial assumption was extremely unlikely. I decided to slow down abruptly to see if the sphere would slow down to stay alongside me. I hit the brakes and slowed to about 20 mph very quickly just as a small hill rose up between my vehicle and the object. It took about a second to pass the hill. I expected to see the sphere shoot forward ahead of me alongside the highway but it never appeared. I looked to the right to the place where the object had previously been and it was gone. I could still see the light from it, though, for another couple seconds. A green glow was reflected off of tree branches as the light moved away from the road. It seems that the moment I slowed down, the sphere made an abrupt 90 degree turn to the right and vanished into the woods. ((ADDENDUM FROM WITNESS)) Yes, I did mean the passenger’s side window. Thanks for the advice. ((END ADDENDUM))

Held as-reported from National UFO Reporting Center (record NUFORC #138517). Witness text is preserved verbatim, including its spelling; nothing is edited beyond formatting.