Hillclimbing (railway)
Hillclimbing is a problem faced by railway systems when a load must be carried up an incline. While railways have a great ability to haul very heavy loads, this advantage is only significant when the tracks are fairly level. As soon as the gradients stiffen, the tonnage that can be hauled is greatly diminished.
Read more about Hillclimbing (railway): Techniques To Overcome Steep Hills, History, Ruling Gradient