Because of the length of the tunnel, an unusual system is used to ensure that the air inside remains breathable and reduce problems with excess fumes. For example, as a train enters the west portal of the tunnel, a red-and-white-checkered door closes on the east portal and huge fans blow in cool air through a second portal to help the diesel engines. As long as the train is within the tunnel, the fans work with reduced power to avoid pressure problems. When the train is approximately halfway through the tunnel, the door opens in earnest.