Section 24: Gradients

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Gradient posts are placed, facing the track, at each location where the gradient of the trackbed changes. Gradients are expressed as a ratio, e.g. "1 in 200" means that the track rises (or drops) one unit in every 200 units travelled horizontally. The angles of the gradient post's arms indicate the direction of the slope [24.1]. Some designs of gradient post omit the "1 in" [24.2].

[24.1] Gradient Post (e.g. Travelling from left to right, the gradient changes from 1 in 105 falling to 1 in 228 falling).	[24.2] Gradient Post (e.g. Travelling from left to right, the gradient changes from 1 in 500 falling to 1 in 600 rising).

If the trackbed is level, the arm of the gradient post is horizontal and bears the word "LEVEL", or just "L" [24.3 & 24.4]. A level gradient can alternatively be expressed as "1 in ∞", since an infinite number of units would need to be travelled before the track will rise or fall by one unit [24.5].

[24.3] Gradient Post (e.g. Travelling from left to right, the gradient changes from level to 1 in 50 falling).	[24.4] Gradient Post (e.g. Travelling from left to right, the gradient changes from level to 1 in 158 falling).	[24.5] Gradient Post (e.g. Travelling from left to right, the gradient changes from 1 in 85 falling to level) (Great Eastern Railway).

Other types of gradient posts have angled bars on a rectangular plate instead of arms [24.6], or separate posts on either side of the line, each showing the gradient in one direction only [24.7].

[24.6] Gradient Post.	[24.7] Gradient Post (Highland Railway).

Where necessary, a gradient post may be fitted with an additional plate indicating to which line(s) it refers [24.8].

[24.8] Gradient Post (e.g. refers to E&F Lines).

Precautions had to be taken when working unfitted freight trains down steep inclines by ensuring that sufficient brakes were applied on the wagons. The trains were required to come to a stand at the top of the incline, where the guard would apply the wagon brakes as necessary before proceeding. After descending the incline, the train would stop again, this time to allow the wagon brakes to be released. Signs were often provided at the top of the inclines where these procedures had to be carried out [24.9 - 24.13]. At some locations, a standard stop board (see [20.12]) was used, with the wording "Stop - Freight train wagon brakes to be applied".

[24.9] Apply Wagon Brakes (e.g. Up direction trains) (GWR).	[24.10] Apply Wagon Brakes (e.g. Down direction trains, with 35 wagons or less) (GWR).

[24.11] Apply Wagon Brakes.	[24.12] Apply Wagon Brakes.	[24.13] Apply Wagon Brakes.

The Severn Tunnel is over four miles in length, with long steep gradients. A short section of level trackbed near the middle of the tunnel is approached from the Welsh end on a 1 in 90 falling gradient and from the English end at 1 in 100 falling. Marker lights, comprising a single blue light [24.14] followed by two blue lights [24.15], are installed in each direction at the end of the falling gradient.

[24.14] Gradient Marker Light (Severn Tunnel).	[24.15] Gradient Marker Lights (Severn Tunnel).

Due to difficulties experienced with the disc brakes fitted to Class 158 DMUs in severe weather conditions, special instructions were introduced in 1995 requiring drivers to regularly test the brakes whilst driving. In addition, special signs [24.16] were provided on the approaches to Druimuachder and Slochd Summits (between Perth and Inverness), and subsequently also at Beattock Summit on the West Coast Main Line. During freezing conditions or when it is snowing (or when fallen snow may be disturbed by passing trains), all Class 158 DMUs are required to make a full service brake application and stop at these signs before proceeding.

[24.16] Running Brake Test Sign.

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