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.
Shorter trains are better on a lot of metrics except the number of crews you need driving trains around, basically. Except that everything ends up taking longer with the longer train, so you have a bit of a false economy, although I'm guessing it's not false enough to make it undesirable.
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.
As a puzzle, suppose ABC is going that way -> and and 123 is going <- that way, each 3 miles long, broken into segments A/B/C and 1/2/3, respectively. Let '-' be the siding, able to hold a mile-long set of cars.
ABC ... 123
`-'
Move C into _, uncouple from AB, and back AB to return to the mainline.
AB ... 123
`C'
Move AB and 123 to the left, past the siding:
AB123 ...
`C'
Uncouple 1, move 23 into the siding to couple to C, and return C to the mainline:
AB1 ... 23C
`-'
Uncouple 23 from C, pick up 1, and move back to the right side of the siding:
AB ... 123.C
`-'
You've now gotten C past 123. Repeat with B then A, leaving the track as 123 ... ABC.
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.
Based on my uninformed reading, these super trains are beyond what the existing rail infrastructure was designed for, and therefore are significantly more likely to derail, while also being more expensive to clean up when they do detail.
Long trains don't "exist" in a way - because the couplers can't hold the weight, so you take a number of shorter trains and mash them together, and then "drive" it like that. It results in all sorts of "fun" that means if everything works perfectly; you save the cost of a crew or two - if anything goes wrong you have a derailment or worse.
Longer trains derail much much easier. For example consider the "straight lining" phenomenon. Straight lining is a major cause for derailments. The straight lining forces are pretty much proportional to the weight of the cars behind the car that is subject to the straight lining forces.
- Shorter trains need less engines (or rather, they can be run with one or two locomotives). That means when one fails the conductor can immediately hear this and halt the train. When a mid- or end engine fails, it may escalate to catastrophic failure
- 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!
Shorter trains are better because they are lighter and easier to control. The additional cars don't just make derailment worse, it causes the derailments to happen at all.
