It's 1986's The Gladiator.http://us.imdb.com/title/tt0091121/
Abel Ferrara made this. From an epinions review: "He fixes up his truck a bit and goes out and tries to get on with his life. However, when a bunch of neds cause him and his truck grief, it pushes him over the edge, and he customises his truck to have a harpoon launcher, and nicknaming himself ‘The Gladiator’ (after Jeff’s footy team) he sets off to bring an end to bad drivers, and hopefully catch the Death Car driver. Naturally this garners the attention of the police, who think he is a mad vigilante, but will he catch the Death Car or will the police catch him? The answer lies in the ‘thrilling’ climax of this movie. "