Factual error: If they are really in the Wichita, Kansas airport, listen carefully to the airport announcements (real faintly in the background). When they say for "Mary Ellen" to meet her party upstairs, there's a slight problem with that. There is no upstairs in the Wichita airport. (00:12:53)
Suggested correction: There is an upstairs. You enter the terminal on the ground floor and go up for security and the gates.
Continuity mistake: The size of the bed in Neal and Del's motel room changes overnight.
Continuity mistake: When Dell and Neal are sitting on the side of the highway in downstate Illinois, the sign says "Chicago 102" in one scene and "Chicago 100" in another.
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)
Revealing mistake: When Steve Martin first calls home to tell his wife that the flight is delayed we see a lovely, cozy picture of the Page family enjoying a delicious, home cooked meal. However, in the shot where the kids are all sitting at the table the youngest child (back to camera) is being carefully 'watched' by a woman who is sitting on the floor next to his chair. I presume it is the actor's mother making sure that her little baby doesn't fall off the chair...
Factual error: At the very beginning of the film during the boardroom scene, Steve Martin checks his plane ticket. Departure time on ticket from NYC is 6:00pm. Arrival time to Chicago is 6:45pm. Travel time from NYC to Chicago is approximately 2.5 hours. Arrival time after time zone change should be approx. 7:25pm, not 6:45 pm. (01:31:25)
Suggested correction: Unsure about plane travel time in the 80s. But it currently takes 90 min to travel from DC to Chicago, and the airlines usually add a buffer. So this trip would most likely arrive at 6:30 CST, and a 15 min buffer time would still be reasonable (6:45 pm). For example, my plane tickets usually say estimated flight time of 1:45 or 2 hrs, but when the air currents are normal, it takes 90 min. DC is slightly further south than Chicago, while NYC is slightly further north.
Suggested correction: Considering from Los Angeles-Chicago is a 4-hour flight, and LA-New York is a 5-hour flight, I don't see how it could take 2.5 hours between New York and Chicago. Seems like 1-1½ hours is more accurate.
Visible crew/equipment: When Neil is looking for the car he hired in the car park, there is a tracking shot from Neil's POV moving along the backs of the cars. On the car in space V-2 you see the reflection of the camera on the dolly and some crew members moving.
Continuity mistake: Right after the close call going the wrong direction on the freeway and Steve Marting pulls his fingers out of the car's dashboard. The following shots show John Candy releases his grip of the steering. The top of the steering wheel has been completely push forward. All remaining shots of the car show the steering wheel in perfect alignment.
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.
Audio problem: As Neil is talking to his coworker about getting on a plane, the audio is either different or synced wrong, as the coworker says something different. In the shot facing Neil his mouth doesn't match.
Continuity mistake: After the train breaks down, the scene apparently takes place in the late afternoon. The sun angle is low in the shots where Del is hauling his trunk across the field. We then see a wide shot and the sun is higher in the sky.
Continuity mistake: Neil returns to the station where he left Del at the end. As he gets off the train and goes into the station, it's not the same station he was at earlier. The background outside shows houses and trees. Where did the buildings of Chicago go?
Revealing mistake: When they are sitting in the bus station in Jefferson City - and then the next scene is the somewhat "speeded up" shot of the kid running up and down the aisles of the bus (before the "take a picture, it'll last longer" scene) - as the kid is running up and down the aisle, watch the woman in the front left seat. The handheld windmill that the kid is running with hits her in the head and her eyes "pop open" as to be surprised by the hit.
Factual error: In Wichita, when Del and Neal are getting picked up by Owen at the Braidwood Inn, there is a mountain right behind Owen. There are no mountains in Kansas.
Other mistake: When Neal checks his airline ticket it says he departs from N.Y.C. J.F.K. but the movie claims to have him flying out of LaGuardia.
Continuity mistake: When Neil is chasing the cab after Del stole it, the bags he is carrying change hands in different shots.
Continuity mistake: When Neal is racing Kevin Bacon for the taxi, he gets close to the cab and all lanes of traffic are at a standstill. Seconds later when he trips over the trunk, the lane he falls into is empty and a car has to brake hard to avoid hitting him, indicating it was travelling at speed already.
Other mistake: To go from Wichita, KS, to Chicago, they would go NE through KS, Missouri, Illinois. Kentucky is NOT on the route. They are pulled over by Kentucky State Police (Lenny). But this is the trip from Hell. Maybe they took the L O N G way East to Paducah, then back North to Chicago.
Continuity mistake: After leaving the El Rancho hotel. (when pulled over by the state police) Neil seams to find some new clothes, including a too small hunting hat, and scarf. On the walk home, Neil is carrying a large suit case, instead of his garment bag and brief case.
Factual error: In the scene at the Braidwood Inn, after Neal shakes Owen's hand and the shot is of Owen with the freeway in the background, you can see a Jays Potato Chips truck drive past. The inn is supposedly near Wichita, Kansas. Jays Potato Chips were not sold west of the Mississippi at the time.