A ventilation system is used to reduce problems with fumes. As a train enters the west portal of the tunnel, doors close 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. After the train has left the tunnel, the red-and-white-checked door immediately closes and the fans operate for 20 to 30 minutes with maximum power to clear the tunnel of exhaust before the next train passes through. In the opposite direction, the door opens when the train is about 0.6 mile (1 km) away from it.

Cascade Tunnel (dlzka 12.5 km - najdlsi tunel v USA)