Did the season for maximum hopper utilization extend through the winter or did it let up as the winter progressed? Did the coal season for home owners coincide with industrial users?
The coal dealers near where I grew up had enormous concrete silos. Were these filled to top during the fall and allowed to empty as the winter progressed? I think unloading a hopper of frozen coal could be a pain in the neck and wet coal might freeze again. So why not stock pile coal before the freezing season?
I've seen photos of many home road hoppers being stored during the summer months. I imagine all off road hoppers are returned as the weather gets warmer. I would guess that the season starts out with all home road hoppers and the number of off road hoppers peaks when coal utilization is at it's maximum. But when is that maximum?
