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 is only possible when the tracks are fairly level. As soon as the gradients increase, the tonnage that can be hauled is greatly diminished.

History

Early tramways and railways were laid out with very gentle grades because locomotive and horse haulage were so low in tractive effort. The only exception would be with a line that was downhill all the way for loaded traffic. Brakes were very primitive at this early stage.

Where a railway has to cross a range of mountains, it is important to lower the summit as much as possible, as this reduces the steepness of the gradients on either side. This can be done with a summit tunnel or a deep summit cutting.

A summit tunnel can lower the summit even more, and steeper hills result in shorter tunnels. Also, tunnels cost the same no matter how much overburden there is, while cuttings tend to increase in cost with the square of the overburden.

Care had to be taken with summit tunnels in the early days of steam with designs that suffered from problems with smoke and slippery rail.

Ruling gradient

The ruling gradient of a section of railway line between two major stations is the gradient of the steepest stretch. The ruling gradient governs the tonnage of the load that the locomotive can haul reliably.

Techniques to overcome steep hills

Some of the techniques that can be used to overcome steep hills are:

Railway layout to reduce gradient

Compensation for curvature: the gradient is slightly eased on sharpest curves so that the tractive effort to pull the train is uniform.
Horseshoe curves
Spirals
Zig zags

Track type

Rail surface treatment
Strengthening the track on or approaching the steep grade, allowing higher speeds, and allowing the train a run at the gradient. This can be used in short underwater tunnels, where there is a steep descent just before the climb.
Fell mountain railway system
Hanscotte centre-rail system
Rack railway
Elevators, cable railways, or funicular railways driven by stationary engines (cable haulage up and down inclines)

Motive power

Using a booster engine, though this is usually limited to starting the heavy train
Using two-in-one articulated locomotives such as the Fairlie, Garratt or Mallet locomotive
Replacing the engine with a more powerful heavier engine for the duration of the steep grade
Attaching additional banking engine(s)
Using multiple units to divide the load on tractive wheels
Geared steam locomotives such as a Shay locomotive
Atmospheric railway^[1]

Modifying the load

Dividing the load or splitting the train, which requires a siding at the summit

References

^ Buchanan, R. A. (1992). "The Atmospheric Railway of I.K. Brunel". Social Studies of Science. 22 (2): 231–243. ISSN 0306-3127.

v t e Railway track layouts
Railway track	Single track Passing loop Double track Quadruple track Crossover
Rail sidings	Balloon loop Headshunt Pocket track Refuge siding Rail yard Classification yard
Junctions	Flying junction Level junction Double junction Facing and trailing Grand union Grand circle / roundabout Wye Switch / turnout / points Swingnose crossing Level crossing
Stations	Railway platform Bay Island Side Split Terminal station Balloon loop Spanish solution Cross-platform interchange Interchange station Infill station
Hillclimbing	Horseshoe curve Zig Zag / Switchback Spiral
Track geometry	Track gauge Ruling gradient Minimum curve radius Cant Cant deficiency