Route availability
System for grading the railway network of Great Britain
Route Availability (RA) is the system by which the permanent way and supporting works (bridges, embankments, etc.) of the railway network of Great Britain are graded. All routes are allocated an RA number between 1 and 10.
Rolling stock is also allocated an RA (again between 1 and 10) and the RA of a train is the highest RA of any of its elements. The train must have a route availability (RA) lower than or equal to the RA of a line to be allowed to use it. The RA is primarily related to the axle load of the vehicle, although axle spacing is also taken into consideration. In practice it is the locomotive which governs where trains may operate, although many high capacity 4 axle wagons have a high RA when fully loaded. (When considering the operation of trains the loading gauge must also be considered.)
The system was first devised by the London and North Eastern Railway, and perpetuated by British Rail to ascertain which locomotives can work on which lines throughout the rail network in Great Britain.
Exemptions may be obtained to allow locomotives to operate on lines from which they may otherwise be banned. An exemption might be granted by placing a speed restriction over a weak bridge, for example.
01Line calculations
The route availability for a line is calculated by taking into account bridge strength, track condition, structural issues and so on. A route availability of one (RA1) is the most restricted line, open to possibly one type of locomotive specially designed for it. A route availability of 10 is the most open, usable by any locomotive that fits within the GB loading gauge that has been 'passed' for it (checked for conflicts with infrastructure such as platforms).
02Vehicle calculations
Route availability for a vehicle (locomotive or wagon) is generally based upon its axle loading. That is, how much of the laden weight of the vehicle is distributed on each axle. The more weight on each axle, the higher the RA number, and the more restricted the vehicle is. For wagons it is normal to have different RAs when running empty and full.
The RA of a locomotive must not exceed the RA of the track except under strictly controlled circumstances.
Thus a locomotive with RA1 is able to work on any line, although it will have a very light axle loading. An RA10 locomotive could only run on RA10 lines, placing severe restrictions on where it can be used.
If a vehicle has wheels that require significant balance weights, often found on steam locomotives, the dynamic loading resulting in what is termed the hammer blow action may affect the RA of the vehicle.
Network Rail currently gives the allowed axle loadings as follows:
| Route Availability | Axle Load |
|---|---|
| RA3 | ≤16.5 tonnes |
| RA5 | ≤19.0 tonnes |
| RA6 | ≤20.3 tonnes |
| RA8 | ≤22.8 tonnes |
| RA9 | ≤24.1 tonnes |
| RA10 | ≤25.4 tonnes |
| EU average | ≈22.5 tonnes |
03Historical notes
Before nationalisation the Big Four railway companies had their own classification systems.
GWR's system for classification featured a coloured disc painted on the locomotive cab side to indicate its route availability:
| Disc colour | Axle load (long tons & cwt) | Axle load (lb) | Axle load (t) | Notes |
|---|---|---|---|---|
| (no disc) | up to 14 long tons 0 cwt | 31,400 lb | 14.2 t | |
| Yellow disc | 14 long tons 0 cwt up to 16 long tons 0 cwt | 31,400-35,800 lb | 14.2-16.2 t | |
| Blue disc | over 16 long tons 0 cwt, up to 17 long tons 12 cwt | 35,800-39,400 lb | 16.2-17.9 t | |
| Red disc | over 17 long tons 12 cwt | 39,400 lb | 17.9 t | |
| Double red disc | 22 long tons 10 cwt | 50,400 lb | 22.9 t | "King" class only |
Sources and credits
This article is adapted from the Wikipedia article “Route availability”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.
Images, from Wikimedia Commons:
- 67028 at Kings Cross 1.jpg by Oxyman, CC BY 2.5
- 86252 Birmingham New Street.jpg by John Griffiths, Copyrighted free use
- Muir of Ord railway station in 1988.jpg by Roger Geach, CC BY-SA 2.0
- Wiliton D9526 double headed.jpg by Geof Sheppard, CC BY-SA 4.0
- BR Class 01.jpg by Johndarm, CC BY-SA 3.0
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