It can be difficult (but not impossible) to do a running brake test at some locations where the grade abruptly transitions from going uphill to downhill with no flatter section in between. I've never been to Tennessee Pass and have never seen a track profile of that line so I can't say if this would be a concern there.
The line I spent the first decade of my career on has several such locations where you abruptly tip over a hill to start down a grade of 2% or worse. My practice in winter was to set the automatic while still going uphill or tipping over (depending on how cold and snowy it was) and then transition to dynamics as the train crested the hill, while doing around 5 mph below the speed limit, maybe slower. As I bunched the train up I would sneak a bit more air off to counteract the potential for an unintentional release, as the leakage and airflow would normally be lower on a bunched train vs a stretched one.
The worst location was the Cardinal River coal mine, whose spur has a 3% grade which goes to exactly one train length from the end of the track. So it was physically impossible to do a running brake test or warm them up in winter before descending that grade. The standard procedure there was to set a minimum application while you were stopped after loading the train, and then release the independent and start pulling. Needing low throttle to start the train meant it would brake normally, if it rolled away without any throttle you knew you would need more air than usual (needing a 14 to 16 PSI reduction from a 90 PSI charge was considered normal on that hill). After a January 2018 runaway we started doing a walking brake test and applying handbrakes on cars that would not set up before descending that grade.
https://www.tsb.gc.ca/eng/rapports-repo ... e0007.html
Around 1980 a different part of our line had a very similar runaway to the one the OP's link describes. Our rock quarry loads their train themselves using their own air supply to roll it downhill one car length at a time, and they use air brake antifreeze in their system. On this day they had for whatever reason used a substandard type of antifreeze, but did not notice as one of our famed Chinooks was blowing in and warming up the quarry site. The train behaved normally as it departed they quarry but soon entered a zone of colder air as it approached one of the aforementioned 2% grades, causing the "antifreeze" to solidify. When the engineer took air nothing happened, the train ran away and everything derailed except for the power, first car and caboose. No one was killed but they were all pretty shaken up.
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DRG-TP.pdf [996.67 KiB]