First go to the options screen [hold square and press up, circle, down, circle, left, right, left, right, circle]. This will open a new menu called "secret menu". Don't go there yet. Now for the second part -> start a single player game and type in NORTHEND as your name. This will open another menu under secret called "Top secret" where you can turn all vehicles on/off. So back out and go into options and you're set.