I can't remember if these have "always" been there, but recently I've been increasingly conscious of the appearance of a certain type of container. White containers with no prominent side markings but two large vents: https://www.flickr.com/photos/129093250@N02/21818942649/in/album-72157659570189485/ at the far right at 0:26 Here's a similar container with only one vent, bearing reporting marks CPPU 90007 at 1:24 These never appear in groups. I was reminded of this photo http://www.railpictures.net/viewphoto.php?id=519153&nseq=0 and wondered if these were also distributed braking containers.
I know that distributed braking cars were used by roads including CP and BN, and their use has been attributed to cold climates. I sort of recall hearing of SP braking cars, though... I noticed that these containers sometimes appear close to a midtrain DPU, which doesn't fit my hypothesis. For most of my railfan life, I assumed that refrigerator cars were self-powered. Then I heard of a Russian setup with four reefers powered by a single generator. Then, with much stronger relation to North American practice, I heard that F40PH in Panama were dual-service locomotives, supplying HEP to refrigerated containers when in freight service. I thought, "If they do that, why doesn't any North American freight railroad?"