Route Availability
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Route Availability is a system devised by British Rail to ascertain which locomotives can work on which lines throughout the rail network in the United Kingdom. The system uses numbers from 1 to 10 and a locomotive must have a route availability (RA) lower than or equal to the RA of a line to be allowed to work on the line.
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.
[edit] Route availability of a line
The route availability for a line is calculated taking in to 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 UK loading gauge that has been 'passed' for it (checked for conflicts with infrastructure such as platforms).
[edit] Route availability of a locomotive
Route availability for a locomotive is general calculated based upon the axle loading of a locomotive, that is, how much of the weight of the locomotive is distributed on each axle in each bogie. The more weight on each axle, the higher the RA number, and the more restricted the locomotive is.
A locomotive with RA1 is the most readily available and general purpose locomotive (although likely to have very limted capabilities), whereas a RA10 locomotive could only work upon a RA10 line.
