 When a freight car rolls down the hump, an analog computer goes to work to control the car's speed.The computer takes into account the car's weight, the kind of bearings, the condition of the lubricant in the journals, the direction and velocity of the wind, on which track the car must come to rest, how many curves it must go around to get there, and how far down that track it will be going before encountering another car.In the time it takes the car to move 150 feet down the incline, the computer has calculated the precise speed the car must leave the hump track in order to roll to its classification track and couple safely with the next car.