"Humping" is a freight train method of taking a train of cars that are all going different directions, and putting all the ones going the same way together. It's done at a specially built switch yard at the top of a gentle hill. The cars are slowly pushed to the crest of the hill (hump)where a guy unhooks each car. The cars then roll down the other side of the hill where more guys are working the switches to put the train together in the way they need to be to continue their trip. They do tend to bang together, so passenger cars aren't heavy enough to take that kind of punishment. I guess passenger cars need to be rearainged from time to time, but hump yards are a dieing breed.
As a railfan, I used to sit at a pizza place across the street Potomac Yard and watch them humping freight cars. It's a damn shame they tore up that yard to build a shopping center.
You'd think sex was involved with all this humping and banging.
