Cascade Tunnel East Portal, Washington

This 7.8 mile long railroad tunnel, at Stevens Pass, in the Cascade Mountains, is often cited as  the longest railroad tunnel in the USA. It was put into service in 1929, as part of Great Northern Railway’s route. It is used by BNSF today, and Amtrak’s Empire Builder passenger train goes through it.  Due to the length, an unusual air circulation system is employed, where doors automatically open on either ends of the tunnel and exhaust fans blow fresh air into the tunnel as the train passes through, to help fuel the engines with oxygen. Then, once the train has past, the fans blow even harder to remove the contaminated air out of the tunnel. It takes around 20 minutes to clear the exhaust from the tunnel. Train operators carry respirators in case of a failure, and there are oxygen tanks at emergency stations spaced every 2,000 feet or so inside the tunnel.