Extreme cold does, can, and has had effects on air brakes, although most properly operated trains, complying with all of the applicable rules do make it, through the mountains, even in extremely cold weather....

Unfortunately, there already appear to be a number of really stupid decisions, as well as rules violations, both regarding the proper use of the air brakes, and with regard to operating on grades like that found in the Canadian wreck, that would make me cringe, even in the "balmy" 110 degree summer weather, one can find on Beaumont, or Cajon, with that power, and a train of that tonnage.

These serious "failures" in rules compliance and possible operational decision-making may have been compounded, as well, by the effects of the extreme cold (gasket shrinkage, ice, stuck valves...) in the operation of the air brakes, or in conditions that contributed to not doing what should have been done (tying handbrakes to allow safe recharge of the trainline), with a train of this extreme tonnage, that was having the problems this train encountered, prior to the runaway. These are all things that we are very likely learn, in detail, when they've completed the investigation.