High Tension

Question: The killer arrives at the farm in an old rusty truck which Maria stows away in with the captive Alex. Then from the gas station she follows the truck in the murdered station attendant's car, and both vehicles end up at the scene of the final confrontation. Yet at the end we learn that Maria is actually the killer and has insanely hallucinated virtually the entire movie. Can anyone offer any explanation of where that big truck came from in the first place and what the truth is about which vehicles were really present at the end and how exactly Maria and Alex arrive at the scene of their final confrontation?

Chosen answer: It is impossible to know which vehicles were actually used, or even what really happened throughout the movie. The plot twist at the end of this film, while certainly surprising, was not very thoroughly planned out. It's almost as if the writer decided at the last minute to add it for no better reason than he couldn't think of a way to end the movie.