If they're each pulling down $100k/year (this is slightly bellow amtrack average!) or ~$50/hour in total comp, 3x50x10 = $1500 right there for none of the support staff - managers, staff back in the control rooms switching signals, staff on call for maintainence issues - and none of the associated costs of putting the staff up in hotel rooms on account of being 10 hours away from home when their shift is over, etc. Spread it out over 300 riders and that's perhaps only $5 for the trip and your 1:100 employee:rider staffing ratio. Not so bad!

Of course, there are also 44 hour routes. Or less popular routes without 300 passengers that are run for political reasons, or because they feed passengers into the more popular routes. Or the popular routes when run off-peak, so passengers can still use the route even if they may occasionally need some flexibility in when they travel. The video suggests amtrack employs 1 person per 4 riders, not per 100! For a route half the distance (DC to New York - 3.5-5 hours) they attribute $25/ticket to labor costs.

You've got stories like this where Japan is keeping open a train station for a single passenger - do you think that route has 300 people on it there? And this is in a country where trains are popular and some routes are packed to the brim in the middle of rush hour: https://www.citylab.com/transportation/2016/01/japan-keeps-t...