This movie is bad, but it is aware of how bad it is. At first, it is just hilarious such as when the killer, as a child, stabs his mom's lover in the back with an obviously plastic knife and he clutches his stomach as he falls over dead.
Later, it gets a bit more interesting. The killer gets obsessed with this girl and follows her. He gets imprisoned, she lands a role in a movie after she becomes well known due to her victim status. The killer breaks out and follows her to the film set where the producer wants to make a horror/porn film and the director doesn't. This shows the director's awareness of what goes on in the slasher genre and allows some interesting commentary, but it also shows that Freeway Maniac is self aware and intentionally bad. That badness makes this possibly the funniest movie I have ever seen.
Later, it gets a bit more interesting. The killer gets obsessed with this girl and follows her. He gets imprisoned, she lands a role in a movie after she becomes well known due to her victim status. The killer breaks out and follows her to the film set where the producer wants to make a horror/porn film and the director doesn't. This shows the director's awareness of what goes on in the slasher genre and allows some interesting commentary, but it also shows that Freeway Maniac is self aware and intentionally bad. That badness makes this possibly the funniest movie I have ever seen.