A question about your "controlled runaway" situation. In such an instance, could or would you then add more air, and back off on the dynamics? Or is that not possible once the scenario is in place?
Interesting how "Butt Crack" applies to many more situations than just trains, for instance flying or driving or power boating or........Etc.
you can always add more air by the pound, but you can not simply knock it off if you used too much. Dynamic braking is opposite, you can smoothly add and reduce as needed.
Most 'idiots' can get a train up the mountain - it takes a ENGINEER to get the train down the mountain SAFELY!