[miander]

This is a really cool tunnel! It's a single tunnel 57km long and the trains are all-electric. There was a nice comment thread a couple months ago: https://news.ycombinator.com/item?id=10465597

[herbst]

I wonder, what else would the train be other than electric?

[samcheng]

Switzerland is awesomely-electrified, but there are still branch lines that don't have overhead wires. Diesel locomotives (actually, the Diesel generators generate electricity that then powers the traction motors) are still in common use all over the world.

[ucaetano]

The cascade tunnel, longest rail tunnel in the US with 12.5km isn't electrified and has only diesel trains running through it: https://en.wikipedia.org/wiki/Cascade_Tunnel

[djcapelis]

Diesel trains are still very common in many parts of the world.

[noipv4]

Swiss innovate a lot in locomotive tech. (ABB and Stadler are 2 big companies that do a lot of electric loco R&D) The TILO (Ticino Lombardia) Swiss trains (S10, Stadler FLIRT) can run on both 15kv AC (Swiss) or 3kv DC (Italy) power systems when they cross the borders. No de-boarding and re-boarding to a different train is required. http://www.tilo.ch/en/Azienda/Treni.html

[rmoriz]

In the US most railway lines are not electrified.

[ianpurton]

Steam.