(Click on the annotation in the beginning of the video to go to the trick)
(After watching this video, I noticed the pig in the hallway close to the window. If that pig can be interacted with, it would be quicker than grabbing the first pig)
This is the very awesome pig flying glitch. This can skip having to fetch the petrol tank, refill it, and bring it to the truck to cause the truck to backfire. The process for this glitch is very simple. Line up the pig in the direction as seen in the video, get on the pig, crouch (hold your crouch button down for this whole trick), grab the pig, and mash jump. Once you have gotten high enough to clear the fence, you can hold forward while still jumping to move over the wall. Once past the wall, simply let go, and you should survive the fall.
*I did not discover this glitch, rather, I learned it from the guys on the SpeedDemosArchive.com forum thread for A:AMFP*