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When you get to those places where it says press X or the xbox 360 equivalent to go over an obstacle, go over then quickly go back, you should be behind the obstacle and the game wont let u over it again, since the game thinks u are over the obstacle and ahead things back in the map start to dissapear such as barriers, using this to your advantage you can get out of maps.
EDIT: I'll post a video of how to do this process correctly soon.