Undesired emergencies were quite a concern on CP Rail in the 1980s, and as I recall mainly on unit coal trains with midtrain power. Allegedly, there were some derailments resulting from the UDEs, which were believed to be caused by "kickers," bad control valves on individual cars that would go into emergency during a service application. Of course the vent valve on the car would expedite an emergency application on the entire train. Some in the running trades believed it may have instead been a glitch in the equipment on the remote control locomotives.

At that time a policy of walking trains after a UDE was instituted. So UDEs had a bad habit of seemingly only occuring at 4AM during inclement weather. I'd figured at the time it may be a critical need sensor installed by head office to make sure we were not sleeping. Regardless, I was on several runs were it occurred four or five times, which was a real bummer when you were paid by the mile and it could take 30 or more minutes for the conductor and brakeman to walk the train from each end.

But on a more serious note, one of the issues I recall about UDEs was depletion of train air when a train would resume its journey before air was fully recharged. Crews were supposed to use the flow gauge and not the air gauge to determine when a train was recharged, but perhaps that didn't always happen, especially after the fourth incident. And having to set a sizable number of hand brakes to hold the train on a grade while charging may have been a factor. Obviously, on the steep grades of British Columbia, this could be a problem. In that era, CP did have some serious derailments that were attributed to run aways. I do not recall how much the UDEs were considered a contributing factor.