What are railway gradient posts?
Gradient posts are installed beside railway lines wherever there is a change in the gradient of the trackbed. Each gradient post within the SCRCA has (or originally had) two arms, one either side of a central support post (see the example from Armathwaite station, right). The angle of each arm is set to give a clear indication of the direction of the gradient:
- The arm is angled upwards if the trackbed rises in that direction.
- The arm is set horizontally if the trackbed is level.
- The arm is angled downwards if the trackbed falls away from the location of the gradient post.
The angle of the arm does not accurately reflect the severity or otherwise of the gradient. That is indicated by the letters and / or numbers painted, fixed or cast on the arm on the side facing the running lines (tracks):
- If the track is level, the word 'Level' or the letter 'L' is shown.
- If there is a gradient, the gradient is given as a ratio in the form '1 in nnn' or just 'nnn' (the latter version being the most common within the SCRCA). The smaller the number ('nnn'), the more severe the gradient.
For more photographs of gradient posts within the SCRCA, see the Structure Type Definition for Gradient Posts.
Why are railway gradient posts necessary?
The drivers and firemen working steam locomotives need to have a detailed knowledge of the line and its gradients so they can ensure that enough steam is available to power the locomotive at all times, but without wasting coal and / or water.
In the past, the guard on unfitted freight trains needed a similar level of route knowledge so that, just before and immediately after each significant change in gradient, he could manually engage / disengage the brakes in the guards van (and, where necessary, on individual wagons along the length of the train).
The Settle-Carlisle Railway was built with a 'ruling' gradient of one in a hundred (1 : 100). This means that the steepest sections of the route climb or fall one unit (e.g. one foot or one metre) for every one hundred of the same units travelled horizontally. Many sections of the Settle-Carlisle line have shallower gradients and some sections are level. However, the infamous 'Long Drag' is an almost continuous thirteen mile 1 in 100 climb from Settle Junction to the south end of Blea Moor Tunnel. In steam days, this presented an exceptionally tough challenge for both the locomotives and their crew.
The drivers of modern diesel and electric trains still need to be aware of the direction and severity of gradients, especially when driving locomotives that are hauling heavy freight trains.
Text and photographs by Mark R. Harvey (© Mark R. Harvey, 2017). Some background information kindly supplied by Dave Harris (the Study Centre Co-ordinator for the Midland Railway Study Centre in Derby.