[fredoralive]

The air brake system is fail safe against accidental disconnection. You can intentionally get around it if needed. Obviously they did something like that here, expecting it to be a safe setup for low speed shunting in a yard...

[msisk6]

All US rail freight cars have a "bleed rod" that releases all the air in the brake system so you can move cars for switching.

Most large railroad yards nowadays are "hump yards" where a locomotive pushes cars over a small hill and they roll down the though a series of switches with a computer monitoring their progress and activating rail mounted brakes that squeeze the sides of the wheels so they roll into other cars at a controlled speed to make up trains.

Smaller yards, like in this story of the runaway, are "flat switched" where a locomotive and man power manually do all this work to put a train together. Back before railroads started reducing train crews the engineer wouldn't need to get out to align switches; they had a "switchman" who would get out and align the switches as needed.

[jvolkman]

And if you ever see "DO NOT HUMP" on the side of a car, this is what it refers to.

Crews also "kick" cars in flat yards which looks a bit more like humping in that brakeless cars roll down tracks on their own: https://youtu.be/zEWE3df6Q2s?t=248

[joncrane]

That is an amazing video. Thank you.

[flyinghamster]

Also, fail-safe only works so far. A parked car needs to have handbrakes set or wheels chocked, since the air can eventually bleed out of the reservoir and release the brakes. The Lac-Mégantic disaster [0] involved insufficient handbrakes set on a train parked on a grade.

[0] https://en.wikipedia.org/wiki/Lac-M%C3%A9gantic_rail_disaste...