Forty wrote ...

I've always thought a lightning powered railgun would be interesting.

Signification wrote ...

I can tell you what those signals are (were) used for...learned the hard way...
I can closely relate to that video railroad track experiment--here is a description of one of my similar 'experiment' (~1988) and the shocking result. My house is a little over 100 yards from a railroad track, two-way tracks, thus four rails. As a teenager, my friends and I enjoyed 'playing' around the tracks, doing things like making art from trains crushing things placed on the rails: ex, one of those 5 cent packs of BB's placed under the teeth of a fork created an 'artistic' piece and made me $5. I also mashed a nickel on the rail--it was wide as the rail and thin enough to tear by hand! BION: double stick Scotch tape held it on the track.

OK, I got off on a tangent here, sorry...

To get back on topic, I noticed one night --sparks-- while dragging some cable across the tracks. Catching my interest, I ran home and got my voltmeter and measured several volts (pulsating DC) across the rails. just as in the video (of which I couldn't understand a word), I eventually hooked a speaker across the rails, getting some really cool 'alien sounding' effects that was quite soothing. As there were two sets of rails, I naturally wired them in series for more "volume" I ended up connecting to the four rails, concealing the wires, and running the wire pair, through a wooded area, to my house, through a window into my room and connected to a speaker--just for fun. I got many sounds and could even determine when a train was approaching. That thing stayed there for years--I had almost forgotten about it. Even when they were converting the double tracks to a single track--I guess this is when the wires were discovered an traced straight to me, since one day (my birthday) there was a knock at my door--I opened the door and the driveway was filled with police cars and a huge railroad company truck (which looked like a train car on tires) was parked in the road. The police asked me if this was my house and did I run that wire. When I responded honestly, out came the handcuffs and I got a ride with a convoy to the city jail house. I was interrogated by the police and railroad officials. I explained why I did this and ,luckily, the railroad guys believed me--the police did NOT want to, but no charges were filed--maybe 'birthday mercy'??

Well, the railroad guys actually became interested and we started exchanging information. They explained their concern, since the rails were actually used as signal wires to control the railside 'traffic' lights. I explained I was only listening. When they were convinced I wasn't trying to control train traffic (or worse), I was released--with a court date.

So...the rails were used as electrical 'wires' connected to the railroad 'lights'. I'm sure all that has changed since thirty years.