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Derailments Caused By Emergency Braking?

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[quote user="schlimm"]Is there any thought about reducing the slack between coupled cars in the US?[/quote] Yes, there has been a passionate desire to eliminate slack, especially in this diesel era of the longest trains.  Slack is a natural occurrence with couplers.  They have to close to the point where the pin drops.  To make sure the coupler gets to that point, it has to go past that point somewhat.  That extra travel to make sure the pin drops is the slack. That coupler slack amounts to 1” per coupler or 2” per coupled joint. Once you introduce that coupler slack, it runs in and out as the train travels over the line.  That run-in and run-out creates rolling shock waves that travel from one end of the train to the other.  The run-out waves can accumulate a tension force to the point of breaking a knuckle or pulling a drawbar right out of a car.  Run-in waves can build compression force to the point of buckling the train or a car frame.  Both run-in and run-out can cause a derailment in addition to damaging rolling stock and causing loads to shift. Because of these shockwaves resulting from coupler slack, a cushioning system is needed to help absorb the force before it can build to the point of causing damage.  This is accomplished by adding spring mountings of the coupler drawbar to the car center sill. This spring mounting adds another 5” of slack per coupler, or 10” per coupled joint. Link and pin couplers had considerable more slack than today’s couplers, and they also had a tendency to override each other vertically with a severe run-in.  They needed more slack because there was less standardization in the coupler dimensions in that era of coupler manufacturing.  Link and pin hardware would not necessarily even mate. In the steam era, slack had a benefit of enabling an engine to start a train one car at a time.  But that has never been the core purpose of slack.  Moreover, that one advantage of slack is not needed in this era. Slack could be eliminated by a feature at each end of a car that would push against a corresponding feature on the adjoining car after the couplers mated.  I am not knowledgeable about European coupler systems, but I believe some, if not all, use this method of eliminating slack.  Whatever slack-elimination system is used, it requires more complex coupler systems.  However, the added hardware would be offset somewhat by the ability to eliminate the spring cushioning of the drawbar to the car center sill.
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