September 2004, driving back to calgary from las vegas.We just got married in vegas 20 september, (thats how im sure it was that date).We set off from vegas early in the morning so that we could get back to calgary in one day,Heading for coutts border crossing, we where around great falls montana on a long dark straight road when i observed a light behind me at distance.Thinking it may be a motorbike or a truck with one light out, i wasnt too concerned.Getting closer to me i thought he's going fast. I wasnt going slow.Then he's gone, when a vehicle turns you can still see the light or the glow from the light but, there was nothing.I dont know how long but it was back, at distance, same as before gets closer then gone.Ive been watching this in my rear view mirror, so my wife is unaware of what ive seen.I get her to turn around in her seat and watch.Light came back, got closer, disapeared again.She thought it was weird too.Light came back and she said "pull over, and we will see what it is"."Not a chance!" I said. Then maybe after 5 apearances in total, it never came back.That was my experience , and by the way there were no road intersections for him to turn off. Scared the life out of me, i didnt know if it was aliens or rednecks.