circumstances. Thus a locomotive with RA 1 is able to work on any line, although it will have a very light axle loading (which will limit its capabilities, for example class 01 shunters are RA 1). An RA 10 locomotive could only work upon an RA 10 line, 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: The information regarding route availability (RA) in this article comes from the British Rail (London Midland Region) Route Availability Guide and the Freight Train Loads Book, both issued in 1969. Several routes will have had their RA numbers changed since that time. * Depending on sub-class, see individual article for details. $ Discrepancy with original data. Historical notes Before nationalisation the Big Four railway companies had their own classification systems. Great Western Railway Each locomotive had a coloured disc painted on the cab side to indicate its route availability: See also Rail speed limits in the United States#Track classes References External links British Railways Board Group Standard for Route Availability (historical) Network Rail infrastructure capacity 2D53 Introduction to Route Availability and tables Network Rail Information GE/RT8006 Assessment of Compatibility of Rail Vehicle Weights and Underline Bridges (live issues) at RGS Online Permanent way Rail infrastructure in the United Kingdom London and North Eastern Railway British Rail numbering and classification systems