So the other day - well, a couple of weeks ago actually but I just remembered to look it up - I had to walk a rail car across the shipyard. I noticed the car had “Do not hump” stenciled on the side, like in this photo.

I’ve seen that before, and always wondered what that really meant. Turns out humping railcars sounds kind of fun.

It seems that when you have a whole bunch of cars in one train, and you need to sort them into different trains, the slow way to do it is to get a little railcar pusher, grab each one, uncouple it from the train, and move it to the new train.

The faster way, is to have a bunch of parallel sidings all come together with switches at the top of a hill (“the hump”). Then you just back down the train over the hill, uncoupling each car at the top, and let it roll down by itself. Hopefully, someone’s setting the switches between each car so that the next one goes onto the right siding. Here’s a video of it.

Sometimes the cars bang into the train at the bottom, even if the yard has retarders on the tracks. So if your cargo is fragile or otherwise not-to-be-played-around-with, you probably wouldn’t want them doing that.

The rail car I was walking behind happened to be an M-140 cask designed to carry spent nuclear fuel. (Lots of pictures here.) I guess I can understand why they don’t really want those just rolling around uncontrolled.

So now I know.