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Comment by kabouseng | Hacker News Reader

Longest freight trains currently run upwards of 2km. You could make trains longer but various issues crop up such as ability to radio reliably the whole length of the train for telemetry and distributed locomotive control. Also the brake line systems typically used (air actuated) becomes a factor as well as safety (can't see the whole train)

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Which country? I'm not a train nut, but 2km seemed middling in the U.S., so I Googled it:

> SMART Union transportation division spokesman John Risch told top rail regulator the Surface Transportation Board (STB) at an October hearing on CSX service problems the average U.S. train is up to 1.5 miles long (2.41 km), but CSX has routinely operated trains two or even three miles long since Harrison took over.

-- https://www.insurancejournal.com/news/national/2017/12/07/47...

And what happens if trains become significantly larger than segments.

Trains cannot occupy a whole track from China to Vienna for themselves, right? You need bypasses, stops, segments, etc.

Edit: typo

Oh wow, had't thought of that, I'm shivering from Factorio PTSD at the idea of handling kilometers long trains !

There's going to be good reasons for why a ridiculously long train isn't worth it when it comes to cost-benefit, but these reasons just seem contrived:

> radio reliably

The cars are physically connected, why couldn't you run repeaters down its length?

Presumably any issue you'd have with sightline radio on a >2km long train now you'd also have with a ~200 meter train halfway through a ~50 meter tunnel.

> the brake line systems typically used (air actuated)

And have N independent break systems with central control. It should be more not less safe, a complete failure of one system could be backed-up by another.

> can't see the whole train

So run CCTV on the same system you're using for the radio repeaters?

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