Factual error: There seem to be modern "Walk" and "Don't Walk" signs at each intersection. This film is supposed to take place in 1952. Also it is mentioned there are "Stereophonic" consoles in the motel rooms. Probably would not find those until at best the late 50s.
Factual error: Carol talks about getting on the "interstate", but the interstate system wasn't even initiated until 1956.
Carol Aird: And do you live alone, Therese Belivet?
Therese Belivet: I do. Well, there's Richard, he'd like to live with me. Oh no, it's nothing like that, I mean he'd like to marry me.
Carol Aird: I see. And would you like to marry him?
Therese Belivet: Well, I barely even know what to order for lunch.