The answer, in short, is "P.S.R." — or precision-scheduled railroading.
P.S.R. is an operational strategy that aims to minimize the ratio between railroads' operating costs and their revenues through various cost-cutting and (ostensibly) efficiency-increasing measures. The basic idea is to transport more freight using fewer workers and railcars.
One way to do this is to make trains longer: A single 100-car train requires less track space than two 50-car ones since you need to maintain some distance between the latter. More critically, one very long train requires fewer crew members to run than two medium ones.
Another way to get more with less is to streamline scheduling so that trains are running at full capacity as often as possible.
All this has worked out poorly for rail workers writ large. Over the past six years, America's major freight carriers have
shed 30 percent of their employees. To compensate for this lost staffing, remaining workers must tolerate irregular schedules and little time off since the railroads don't have much spare labor capacity left.