I know this site likes replies with small poems but I'm unable to do that. I was hesitant before to write anything–this last season, but I do want to say I think your haiku is really fresh and creative.
the vast west
railroad cars decouple
in the dark
Expansive to individual train cars being decoupled, but in the dark, where sounds may be sharper, even resonant of things in the past, from the Wild Wild West to train disasters in peacetime and in war.
My father only told me once about the time he picked up pieces of comrades, other soldiers, and civilians, in complete darkness during WWII:
my father's war
a story of the dark
collecting its own