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Comment by js2 | Hacker News Reader

Huh.

http://en.wikipedia.org/wiki/Slack_action

"Loose coupling is necessary to enable the train to bend around curves and is an aid in starting heavy trains, since the application of the locomotive power to the train operates on each car in the train successively, and the power is thus utilized to start only one car at a time."

An example at 2:20 in this video:

http://www.youtube.com/watch?v=9D9zE6mju48&t=2m20s

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So how do you get a locomotive started when the engine and cars are not on flat track? If there is any kind of incline, you'll have no slack in the couplings.

Can you use the brakes somehow?

I'm guessing you answered your own question. If they put the break on the last car, they could let the train compress backwards before starting. Naturally it would still be more work than starting from flat though, so obviously there would be an incline limit beyond which a given train couldn't start regardless.

Can the last car's brakes hold the weight of all the cars in front of it? Can the conductor apply each car's brakes independently?

Interesting stuff!

The original article stated that a train wasn't able to start because the caboose's brake was on, so presumably the answer to the second question is yes, at least for that car. Presumably the first question would depend on the slope of the incline (although if necessary other brakes could be engaged after their cars' couplings were compressed). Anyway, all just conjecture on my part!

You use sand to generate grip, releasing the brake gently and apply power/throttle slowly. If you open the throttle too much, the wheels will spin and you'll damage the locomotive. Don't apply enough power/throttle and the train will roll back down. It takes skill but is honestly no different driving a car and doing a hill start. Same technique.

Edited to add: https://www.youtube.com/watch?v=P3660SX1_oE

This is a Garrett type locomotive on the Welsh Highland Railway. They are the most powerful steam locomotive type on 2ft gauge. Beddgelert station is on quite a gradient and makes for a challenging restart.

The slack action from a mile-long train is one of the most awe-inspiring, bone-jarring manifestations of raw power I have ever experienced. The first time I felt it, it established in my mind the idea that freight trains are forces of nature rather than vehicles.

Passenger trains also experience it (though the gear on these trains are slightly stiffer), but those cars are designed to have a much smoother ride, and they are also much shorter (8-10 cars instead of 80-100+). On a long train, it sounds like thunder coming from the front, and then a split second later the entire world shakes.

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