The idea that one cannot start a heavy train without taking slack is a railfan
myth in today's context. In fact I'd go so far to say that you canNOT use slack
to start a heavy train today. In the old days of cold brass bearings and slow
releasing air brakes you could use the take-slack method to start a train but
not anymore. Roller bearings and faster releasing air brakes has made
slack-starting on a grade impossible. To use the slack method you need to be
able to get the entire train moving forward before the rear end cars release.
If you don't then the rear end will roll backwards and you are going to be in
two (or more) pieces. To prevent breaking in two while starting you can only
accelerate (stretch out) the head end at a certain rate or you will break it in
two from jerking the cars into motion. With todays fast releasing brakes the
brakes will release faster than you can safely stretch the train. Thus you get
the roll back and kapow!. Besides, slack starting one car at a time is not
necessary and has not been necessary since the 1960s. If you have enough loco
power (Tractive Effort) to pull the train up the hill then you've got more than
enough power to start the train entirely stretched, no slack. In my 41 years as
an engineer I've routinely started hundreds, maybe thousands, of tightly
stretched 15,000 ton trains on 1%+ grades with no problems. It is all just
physics. Lighter trains on steeper grades like 2% are similarly started without
slack. Tieing handbrakes on the rear cars to hold the slack in today would be
impossible. You can't walk across the tops of cars to set & release hand bakes.
There is no caboose & thus nobody back there anyway.
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