During the Jail Break mission, you must drive a prison transport to the prison. When you get there, a gate will open Stop in the way of the gate so that it cannot close, and do not completely enter. There should be a gray school bus to your left marked "Prison Transport System" on the side. Get into it, drive to the garage, and store it. Quickly get back to the prison and into the transport. The mission will continue as usual, but you ,ust break through the rest of the three gates yourself. They are easy to break; just drive through them. Note: This vehicle is only available once.