Quote:

Duckassist probably from Wikipedia
The longest railroad tunnel in North America is the Cascade Tunnel, which is 7.8 miles long. It was opened in 1929 and primarily serves freight traffic, with some passenger service.

Note: DDG is wrong. The Mount Macdonald Tunnel in Canada (completed in 1989) beats the Cascade Tunnel handily at 9.1 miles. The Mt. Macdonald Tunnel was never electrified, and was built with forced ventilation suitable for diesel locomotive use. No regular passenger service uses the tunnel.

"Some" passenger service in the Cascade Tunnel consists of one Empire Builder (Amtrak) daily each way. The freight railroad complains at times about the amount of track space that takes up.

The Cascade Tunnel was electrified when it was built, but at the time steam locomotives generally powered trains and nearly 8 miles was too long for them to safely work through the tunnel especially upgrade eastbound (summit near the east portal). Electrics hauled the entire train complete with (idling) steam locomotive through the tunnel. With the advent of forced ventilation trains can run through using just the diesels.