Plot hole: In the final scene where they all leave along the passage; the father rolled out on a stretcher and the others casually walking out, you can tell by their smooth passage along the corridor that all the dead bodies have been removed, but this would have taken at least half an hour if not longer, so it would make no sense in reality for them all to wait for all the bodies to be removed before they left as they would have been the first to leave due to the traumatic experience they had just been through.
Plot hole: For the murder on the highway to happen, the killer (who is not a mastermind, but someone who has a daily job and who never killed before) had to sabotage the car of the victim in such a clever way that he'd stop at a specific point and time (so, predicting also he'd escape out of town and do it through a certain route, which he had no way to predict), and that he'd react to the mechanical problem waving at passing cars walking in the middle (literally in the middle, not the side, or the emergency lane; perfectly in the middle of it) of a highway, where he can drive his semi into him - all while the fog is incredibly thick. Needless to say, it is all a bit too convenient.