Why don't freight trains have cabooses anymore?
Don’t need ’em, and besides, it’s cheaper this way. There used to be two guys in the caboose: the conductor and a brakeman. The conductor did paperwork, the brakeman threw switches, and they both watched for “hotboxes” (overheated freight car wheel bearings). They also radioed useful tidbits of information about the train (e.g., there’s been a little accident) to the engineer. Today virtually all mainline switch-throwing is done electrically from the central office, roller bearings have eliminated most hotboxes and trackside infrared sensors catch the rest, the conductor can do his paperwork in the locomotive, and the useful tidbits of information are provided to the engineer by a soulless machine (see below). So it’s curtains for the caboose.
What you see instead on the end of the train is a gizmo called an “end-of-train device” (ETD) that (1) senses motion, (2) monitors the pressure in the air brake line, and (3) automatically radios its findings to a receiving unit in the locomotive. Unlike car brakes, trains brakes are released by increasing (not decreasing) the pressure in the brake line. This can take a while in a mile-long freight. When the engineer wants to start the train, she pumps air into the brake line until the rear-end gauge reaches a certain level. That tells her all the brakes throughout the train have been released and she can give that puppy some gas.
The motion detector, as you might surmise, lets the engineer know when the back of the train is moving. The significance of this will not be apparent until I let you in on a key fact from my vast storehouse of railroad lore: you can’t start a whole freight train at once. Too much inertia. Instead you have to start it one car at a time, taking advantage of the slack in the couplers that connect the cars.
Before starting, all the cars in a freight train are bunched up behind the locomotive. When the engineer opens the throttle, the locomotive starts moving solo until the slack in the first set of couplers runs out, whereupon the first car in the train starts with a jerk. An instant later the slack in the next set of couplers runs out and the second car jolts into motion, and so it continues all the way back through the train. Eventually the last car starts moving and the motion detector signals the engineer, who can then lay on some serious horses. (If you pressed the pedal to the metal too soon, you might start the last car with too much of a jerk and break the coupler.) If more people knew stuff like this, the country would be a lot better off.
Send questions to Cecil via email@example.com.