So if I understand this correctly, shorter trains are better because when they derail they take down less cars? Or are super long trains harder to control in varied terrain? Both probably.
To mention an issue that I don't think was well-touched upon in the article -- in a lot of places, you have single tracks running from point A to point B, with the occasional side track a train can park on to let another train past.
But these side tracks may only be a mile or so long -- what happens when two three-mile trains need to pass each other using a 1 mile side track? A fun puzzle, but not very fun to implement the solution in real time.
ABC ... 123
`-'
AB ... 123
`C'
AB123 ...
`C'
AB1 ... 23C
`-'
AB ... 123.C
`-'
This solution limits the maximum length to 3 miles. A 4 mile long solution would keep 1 coupled to 23 while moving C from the siding back to the mainline.
- long trains have issues with brake apply speed - remember, train cars are dumb. No electricity, all they have (at least here in Europe) is one main brake line where the transmission speed is the speed of sound - that means, for a 700m long train a drop in pressure at the front is only registered after 2 seconds at the last carriage.
- long trains are a nightmare to shunt around. Not just because you have immense distance between the engine and the conductor at the end, but especially if the train has to run over a street level crossing. Old shunting yards simply were never estimated to run such long trains.
- long trains are a nightmare for residents along the lines for the same reason
- long and especially double stacked trains put up a hell of a lot more stress on the infrastructure than it was constructed for - remember again, this infra is sometimes well over a century old!