Zark's got me beat.

Although, I once had a 13,000 foot "hospital" train (bad orders and junk for scrap) westbound out of Indio, much of it bound for Purdy. It was a disaster and we died, without even making Colton.

We finally had two sets of helpers, including the beet helpers, cut in just to get the damned thing started at Hugo, and probably never had proper air pressure in the caboose, the whole trip, since the damned thing leaked like a sieve. And, the lead engine of the junk train consist had such poor pressure maintaining, that this and the excess leakage caused me to nearly come to a stop at Beaumont, just because of the air test. Thank goodness I had the beet helpers cut in, so we had enough dynamic to control the train going down the hill, which wouldn't "balance" on a set, worth a damn.

Experience with experiments like the 400 car coal trains on the Pennsy ranged from interesting to near disasters. BNSF and UP have tried this "double up" operation (two trains effectively coupled together) from time to time, with generally poor results. Drawbars, knuckles, and dead trains have been the usual result of trying to operate trains which are "too" long, which ties up the RR, and thus tends to negate supposed capacity and crew savings.