It is huge because it greatly helps to maintain the ratio of active participants to retirees.
Central States got upside down when the union freight industry, its largest participant, collapsed in the wake of deregulation and then NAFTA to a smaller degree.
I get yelled at when I say it, but pension funds are similar to ponzi schemes in the respect that they require someone to take the spot of the individual leaving to remain solvent as a result of what's termed "ongoing liability".
....or maybe I'm just a dumb truck driver that doesn't understand economics and actuarial calculations.