While driving east on the interstate 92 the main interstate east west through Montana from Washington state. Anyway to the south from the highway a large white light that lit up the entire hillside to the south traveled east with my vehicle. It looked like day time on the ground in the area of the light. I though it was a chopper but the light was to bright and made no noise. I panicked and started traveling at a high rate of speed and the light just stayed to the south of the highway. It was there for about an hour and then stopped moving as I travel further east. there were no cities or towns where I was, No exits from the highway. I was scared to death. It was not normal what ever it was.