Factual error: After the terrorists on the motorcycle take off, Gordon uses a fire axe to puncture the natural gas line. The natural gas (which was under pressure) would have quickly filled the tunnel. Now when the motorbike drives through it, the engine should have revved high with a combustible gas being taken in in place of oxygen. It would be like using nitrous on a hot rod. But you can hear the RPM's stay normal for a motorcycle.