When the car catches fire there is a sign which reads "Chicago 102 miles" but they drive the car to the motel, then drive it the next morning until they are stopped and the car is impounded. Then when they are in the back of the 18 wheeler, Del looks at his watch and states that they'll be in Chicago in 3 hours.
When John Candy arrives to pick Steve Martin up in the semi truck in the end of the movie he has a black eye. There is no scene depicting it or explanation as to why or how he got it. It's never mentioned, but he has it the last 20 minutes of the movie.
Outside the Braidwood Inn, Neal tells Del that he has a Visa Card, a gasoline card and a Neiman Marcus Card. However, earlier when they check into the motel, Neal pays with a Diner's Club International card.
After Del and Neal drive their rented car between and sideswipe the two semi trucks it is shown that Del has bent the top of the steering wheel down, nearly in half. In subsequent shots, after the car fire, the steering wheel is shown again as being fully round. This is especially noticeable when Del drives the car out of the motel room after backing into the room.
When Del begins driving the wrong direction on the freeway you can see smoke rising in the back seat from his cigarette, but then as the occupants of the other car are yelling at them, the smoke is no longer seen.
When Neal checks into the hotel and leaves Del in the car, it is snowing on Del as he sits in the car talking to himself. When the camera cuts to Neal looking out the window at Del, no snow is falling.
Del and Neal's departing flight is clearly an American Airlines twin-engine jet taxiing on the runway. An exterior shot of their plane in flight shows a four-engine, earlier generation 707 jet with a red and white paint job more TWA-esque in color scheme.
When Neil and Del are on the bus to St. Louis and Neil starts singing, they are clearly driving through an area without trees. But when everyone turns back to look at him they are surrounded by trees and when they go back to Neil and Del, there are no trees to be seen.
After Neil yells at Del Griffith in the Wichita motel, it shows Del Griffith sit back down on the bed with the lamp behind him turned on, then it goes to a shot of Neil, but when it goes back to Del Griffith the lamp is turned off
When the train breaks down Dell is see dragging his trunk away from the train lid side up. Next shot of trunk it is upside-down then right side up and finally when Neal grabs it upside-down again. Dell also has many more people right next to him when Dell grabs the trunk than the immediately preceding shot.
In the second motel, when Neal and Del are drinking and talking, Neal finishes a little bottle of gin and then starts drinking a tequila Del threw over to him. But when Neal toasts the wives, he has gin in his hand again.
When Neal is walking from the parking lot (where his rented car should be) to the main terminal, a brief clipping indicates that the sun is going down. However, when Neal is at the terminal, it appears to be mid-afternoon.
When Neal Page and Del Griffith check into their hotel room at the Braidwood Inn, Neal notices that they have to sleep together in a queen sized bed. Yet they wake up in each other's arms sleeping on a twin or full sized bed.
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.
When Del almost crashes the car because both his parka sleeves are caught on car parts while he was trying to take it off, Neal states that it's hot and suggests he take his parka off. Del agrees, but the very next shot shows Del driving the car again wearing his parka.
When the two men are driving the burned-hull car, they appear to be stopped by a Wisconsin State Trooper. However, if they are driving from St. Louis to Chicago, there should be no need to go through Wisconsin. I-55 should be a direct route from St. Louis to Chicago.
After Del exits the off ramp and starts heading the wrong way on the highway, you can see raised dots on the centerline of the road - something not found in the Midwest as snowplows would rip them off the road.
When the Semi truck they are riding in approaches Chicago and it shows the skyline, it is showing the architecture of Sears Tower as if looking at it from the Southeast. There is no highway that comes from the southeast, that would be in the lake. Other visible buildings are in fact facing another direction than what they are in the movie.
When Del and Neal arrive in Saint Louis by Bus there is an exterior shot of a Trailways Bus Terminal. This Bus Terminal is actually the one in Chicago in fact it happens to be the same one seen in The Blues Brothers.
When Del and Neal meet Gus' son in front of the hotel, they shake his hand. In the background, as Neal shakes his hand, there is a Jays Potato Chips semi driving past. Jays Potato Chips are not sold in Kansas. They are Chicago-based and are not sold west of Iowa or Missouri.
Del and Neil travel in a hire care from St Louis to Chicago but it seems like they are traveling for a very long time indeed. Long enough for it to get dark. Granted it is meant to be in the autumn/fall but even then. St Louis to Chicago is only 4.5 hours away in the car and it is a single interstate road to get there.
Del and Neil travel in a hire care from St Louis to Chicago but it seems like they are traveling for a very long time indeed. Long enough for it to get dark. Granted it is meant to be in the autumn/fall but even then. St Louis to Chicago is only 4.5 hours away in the car and it is a single interstate road to get there. Considering after the car goes on fire and they have to spend the night in a motel, they travel for a bit more but then in the truck they still have 3 hours to go! Highly improbable that all those incidents happened within the space of the first 1.5 hours from setting off from St Louis.
Two comments address the fact that the state trooper who stops Del and Neal is wearing a Wisconsin badge. According to the Director's cut of the movie, this was a scene that was filmed to indicate that they had gone too far, but, due to cuts, that dialogue was removed from the scene. Also, the motel they stayed in the night before was actually north of Chicago, another nod to the same idea (that the two of them had already traveled too far.)
When the L train is coming back to the station at the end of the movie there is an aerial view of the actual train which uses reversed footage. On the ground below you see (very quickly) a person walking backwards.
When Neal and Del are driving on the wrong side of the highway a couple in a gray car try to yell to them that they are going the wrong way. They are supposed to be traveling at highway speeds, but close up on the couple clearly shows the car is in park.
On the bus the child running up and down the aisle accidentally conks the woman sitting in the front seat hard on top of her head with the handle of the toy he is playing with. Watch her eyes to see both how startled she was and also, to her credit, how determined she was not to let it show.
When traveling by car, Del adjusts his passenger seat via power controls while complaining about the position. Later when he is driving, he catches his parka on the controls but now they are manual controls.