If you want to know more, research "precision railroad scheduling" in your news outlets of choice. It's railroad's version of "just in time" manufacturing -- basically squeezing every dollar of value out of the railroad that you can.

This means if train A is scheduled to go from city B to city C, it absolutely positively can not be delayed, or the effects will keep rippling for days, because there's no margin or buffer at all.

That's why they're fighting sick days so hard. If someone calls out sick with no notice, it costs the railroad way more than the value of that person's salary for the day.

Of course, they could fix this by hiring more people, but, PRS is why sick days is such a sticking point.