Continuity mistake: During Neal's family eating dinner, the kid who says "I prefer noogies" is holding a fork in his hand. When it cuts, the fork is suddenly on the table. (00:06:30)
Continuity mistake: When Steve Martin gets off of the train in Chicago near the very end of the movie to search for John Candy in the depot, the part of his hair is on the opposite side (left) from where it normally is. There is no apparent wind blowing his hair - it looks neatly parted on the "wrong" side. When he enters the depot, the part in his hair is back to the "correct" side. (01:23:30)
Continuity mistake: When Del pulls out his wallet and shows his shower curtain rings to Neal, we can see Del's sleeve is pulled up exposing his watch and most of his wrist. When it cuts, the sleeve covers his watch and wrist. (00:09:50)
Continuity mistake: When the boss puts his hands on the table at the beginning, between shots they go from being spread apart to very close together.
Continuity mistake: In the beginning when Neal's boss is looking at his work there is a wide shot showing the man sitting in front of Neal writing on his paper. When it cuts to facing the man he isn't writing anymore. (00:01:10)
Continuity mistake: When Owen arrives at the hotel to meet Neal and Del to drive them to the train station, Owen is wearing gloves on both hands. As he introduces himself and shakes their hands, Owen's right hand is now bare even though there wasn't enough time to remove the glove. (00:33:55)
Visible crew/equipment: When Del is trying to negotiate for a room at the El Rancho motel, part of the boom mic pole enters in the upper right corner of the frame (matted widescreen version of the film, not just the open matte 4:3 version). (01:09:05)
Visible crew/equipment: When Neil exits from the airport just after the employer told him "You are f***ed", some onlookers and a crew member moving the camera on the dolly track can be seen reflected on the glass of the entrance from which Neil comes out.
Answer: The reason was that the snowbank was on his side (the passenger side) when it should have been on the driver's side if they were driving in the right direction. Also and I'm not sure if you could see this in the film but the deflecters on the road which separate the lanes if you are going in the right direction shine yellow and if you are going the wrong way shine red.
Tobin OReilly