In the early 1980's, while riding the Rabbit between Houston and Lufkin on a northbound freight train, the unexpected happened.
I was working the caboose and a friend of mine was working the head end. As we were highballing thru Livingston Texas our train went into emergency. The routine in this situation was that the Head Brakeman started walking back towards the rear of the train and the Rear Brakemen started his trek from the rear to the headend. We did just that!
After meeting about halfway, we were perplexed about what happened. We could hear the trainline air supply started to pump up indicating that the trainline was still in tact. So what the heck happened?
My fellow trainman and I continued to survey the condition of our train and we noticed that a box car was leaning slightly and the main line had a little dog leg...a sort of U shape! We got to looking around for a causation and discovered a deep ditch was full of Bulk Head Pulp Wood Cars with Loaded Rock Hoppers on top of them! It was a mess!
Later it was determined that someone had taken the Hand Brakes off of the cars in the runaround and apparently enough of the air brakes on the cars bled off to allow the cars to roll. As we were going by the runaround, the vibration of our train initiated movement of the cars and they rolled into the side of our train and the cars piled up in the ditch.
I suppose we should consider ourselves lucky. If the cars had rolled out prior to our arrival, we would have hit them head on!