more sources of traction power, at least one of which is external. *B A high-speed unit is one capable of operating at speeds above . Allocations made prior to the introduction of the GM/RT2453 standard were not changed. See also For further information on individual classes of locomotive or multiple unit, see these pages: List of Non-steam British Rail classes Steam locomotives of British Railways Locomotives of the Great Western Railway Locomotives of the Southern Railway Locomotives of the London, Midland and Scottish Railway Locomotives of the London and North Eastern Railway British electric multiple units British railcars and diesel multiple units Related pages on BR numbering and classification include: British Rail TOPS first arrangement British Rail Regional Multiple Unit Numbering British Carriage and Wagon Numbering and Classification Route availability List of British Rail power classifications References British Rail numbering and classification systems Locomotive classification systems British Rail rolling stock