In the Rockies, about to enter Moffat Tunnel

On board Amtrak's westbound California Zephyr, in the Rocky Mountains. We are about to enter the Moffat Tunnel. The Moffat Tunnel is a railroad and water tunnel that cuts through the Continental Divide in north-central Colorado. Running 6.2 miles from its east portal to its west portal, it sits at over 9,200 feet above sea level. During this stretch passengers are told to remain in their car, and not open the end doors. This is because of diesel fumes inside the long tunnel.