Route availability

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). == Vehicle 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: ==Historical 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: ==See also==