Continuity mistake: On the truck cab's rear window, there is some sort of air conditioning unit installed. In some shots, such as the gas station scene where David Mann is on the telephone, or the railroad crossing scene, the air conditioning unit has a support structure to hold it in place. In the rest of the film however, there is not any support structure to be seen.
Continuity mistake: When David Mann crashes his car against the truck near the end of the movie, the car's frontal bodywork inexplicably returns as brand new in one shot and back smashed again.
Continuity mistake: When David crashes his car into the fence at Chuck's cafe, it shows that it was the passenger side that crashed into the fence. The driver side is undamaged. However when David exits his car to help the bus driver, there is significant damage to the driver's side of his car. (00:26:40 - 00:44:25)
Continuity mistake: When David has the accident and crashes his car against the fences, he steps out of it and closes the door, but when he comes back to go on his own way, the car door is inexplicably open. (00:26:49 - 00:42:52)
Continuity mistake: In the first scenes when Weaver first encountered the truck he is pictured in various states of seatbelt wearing. In some scenes it's down and across, in others nothing.
Continuity mistake: Towards the end of the movie where David begins to take advantage over the truck driver, and he turns on right towards the climb also breaking the cartels and fences, the weather changes in two shots: it's cloudy before and sunny immediately after.
Continuity mistake: After the truck tried to make David's car hit by the train dabbing it from behind, the car has a dent on the right rear light, but in a following scene, the dent has vanished. (00:53:09 - 00:54:30)
Continuity mistake: Visible on the theatrical release. After David has overtaken the truck, you can see from the interior shot that David has his seat belt on. A few seconds later in the external shot David is no longer wearing his seat belt. (00:08:10)
Continuity mistake: When David returns on his way after sleeping, he first wears his glasses in a shot, but when he suddenly brakes after seeing the truck stopped on the side of the highway, his glasses are gone. (01:03:07)
Answer: At that point in the film, the protagonist David Mann is ready to confront the truck driver. When he sees the old Peterbilt truck outside, David mistakenly assumes the truck driver has already entered the diner, so he confronts a likely suspect that he sees at the counter (but he has misidentified the man). The misidentified man takes offense and punches David out. By the time he recovers his senses, David sees the old Peterbilt truck leaving the parking lot. Which means the actual homicidal truck driver never entered the diner in the first place and was waiting outside the whole time. If David had first gone outside to the Peterbilt, there was a good chance the waiting homicidal truck driver would have killed him right there, and the story would have abruptly ended. So, David's misidentification of the truck driver allowed the film to move ahead into its next act.
Charles Austin Miller
Yes, I get why the filmmakers did that, but I still think it is a plot hole. If the Dennis Weaver character was afraid of getting killed by the truck driver, I doubt he would have confronted him in the cafe.