Ok, sounds I got incredibly lucky with two interchanges then :-/ I’d actually bet it’s not fully random either, but depends on both the map and the length of the game.
On that last screenshot the orange line isn’t really carrying its weight; it’s never delivering anything, just building up a backlog. I would probably rather have extended the red line east instead,. Or at least connected the orange between a circle and a triangle, not two circles.
But even in this situation, it seems like once things started piling up on that station, you could just have moved another train to the red like temporarily. Feels like either orange or the single carriage purple could have gone away for a few trips without causing a disaster. Or even 5 seconds before the end, the blue double carriage could have gotten that city under the limit with a single load. Unlike the other screenshots, there really was just a single crisis spot.