An example: Trains snaking across undulating terrain are like Slinky toys. On the way up a hill the cars pull apart; on the way down their tendency is to crunch together. GE Transportation's new Trip Optimizer is a smart cruise-control system that knows the slope of the hill, the length and weight of the train, its contents and its braking ability. It then automatically regulates the train's speed to maximize its efficiency and consume the least amount of fuel.