Chicago Noir: 1942

This a hump yard, where a locomotive pushes cars up a small hill (behind the camera) and the cars are uncoupled individually or in groups to roll down the other side of the hump to their respective tracks. The thing on the ground around the rails is a pneumatic retarder that slows the cars to a safe coupling speed by gripping the wheels. The switches are controlled by the towers in the photo. It's an interesting operation to watch.