We just swapped a 39’ stick at MP 212 around 3 a.m. — four of us on the tongs, lungs burning — and it got me wondering: was that length just to fit 40’ flats or did some clearance law or curve math set it? Curious what the old heads were taught.
Mostly a loading limit: 39’ was the longest you could ship in a 40’ flat/gon without fouling clearances on curves — “fit a 40’ car” was the rule of thumb — and it kept a stick just manageable for a four-man gang. Earlier you’ll see 30–33’ rails, and a few roads tried 39’6", but ARA practice settled on 39’; the couch-through-the-door problem. If you want chapter and verse, check early ARA/AAR open-top loading circulars from the 1910s–20s — were your joint bars 24" or 36" at MP 212?