Norman says they moved the highway yet when Norman is standing out by the swamp after the murder of Arbogast, Sam Loomis calls for Arbogast, and in the background (on the top-left) of the screen you can easily see a truck drive by in the distance. Apparantly that was a Universal Studios service truck that crept into the movie.
Ok so you're saying there shouldn't be a truck out here because Norman said thet moved the highway? Is every road a highway?? There could quite credibly be another road near the Bates Motel where a truck could be making a little night journey.
Just because they don't use that road as the highway anymore doesn't mean vehicles don't travel along the road still. How do you think Marion or anyone else got to the hotel?