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 increase, the tonnage that can be hauled is greatly diminished.
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.
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.
Some of the techniques that can be used to overcome steep hills include:
The pioneering Liverpool and Manchester Railway was built at a time when choice between locomotive and cable haulable was not clear cut. Therefore, all hill climbing (1 in 100) sections was concentrated in one place where cable haulage by stationary engines could be used if necessary, while the rest of the line was engineered to be so gently graded (say 1 in 2000) that even primitive locomotives would have a chance of succeeding. As it turned out at the Rainhill Trials of 1829, locomotives proved capable of handling the short 1.6-km length of 1 in 100 gradients on either side of the Rainhill level.
Since the early trains had primitive brakes, it was also necessary to have very gentle gradients to reduce the need for strong brakes. Sudden changes in gradients would have also overstressed the primitive couplings between the carriages.
The gentle 1 in 2000 gradients were made possible by very substantial earthworks and bridges.
The Redruth and Chasewater Railway, a narrow gauge route across the Cornish peninsula (planned in 1818, opened in 1825) used a significant incline to access the harbour at Portreath, which like many in Cornwall sits in a steep valley.
On the Lancaster and Carlisle Railway (L&CR) of 1847 a deep cutting was cut at the Shap Summit. This cutting was cut through rock, about 0.5 mile (800 m) in length, and is between 50–60 feet (15–20 m) deep.
On the Docklands Light Railway the entrance to the tunnel from the original London and Blackwall railway viaduct to the tunnel to Bank has the steepest gradient on any British railway at 1 in 17 (5.88%). A zig zag stripe has been welded to the rail surface to allow trains to gain a satisfactory grip, and prevent slipping.